Farewell, but not forever.
Hasbro Jem items were no longer produced after 1987 and thanks to massive clearance sales, most stores were bereft of Jem items by Christmas of 1988. There are a handful of items with 1988 markings that were available by Hasbro licensees, for a short time in various countries; the cartoon ran new episodes into 1988, and that was the end of Jem. It was aired in reruns for another few years in the US and Canada; other countries in South America and Europe aired Jem sporadically for the next decade or so. 

1988-2003: The Great Jem drought

1988-1990 (?): Jem comics are sold in Mexico.

The only official merchandise available at the time elsewhere, were
Jem-themed T-shirts & similar items (though how "official" they were is still up for debate) available at stores like Hot Topic, starting around 1997 or so, and on the home entertainment front:

1998 - SPICEJem series of VHS available in Sweden.
1999 - In the US/Canada, VHS releases of Passport to Rock, and Fashion Fiasco
2003 -
Film Factory AB in Sweden releases Truly Outrageous! the movie on DVD.

Unofficially, Precious Jems, a mailed out fanzine of sorts was an early means for fans to share information, then with the popularization of the Internet, fan sites sprang up- the Truly Outrageous Mailing List particularly being instrumental in joining Jem fans all around the globe together. As today, there were also piles of unofficial, home-made items available on sites such as eBay. Prices for mint and boxed Jem items climb ever higher.

2004 - 2010: Rhino gives it a shot, Jemcon begins.

In late March of 2004, excitement builds as Rhino releases the first of the digitally enhanced, Dolby 5.1 versions of what would eventually be only two box sets. The final third never materialized. The enhancement process made the graphics very bright and crisp, though Pizzazz's hair unfortunately didn't translate too well, and it turned an unappetizingly drab orangey shade. There were a few glitched up songs as well, but for the most part Jem fans were too desperate to do much else than grumble about it as they forked over the money anyway. To sweeten the pot, there was an extras disc with interviews with Christy Marx and Samantha Newark included, as well as commentary on a couple of episodes and some excerpts from the Jem bible.
Various European markets were subsequently treated to DVDs in various languages and formats, with France, in 2010, finally being the first country to supply us with the full 65 Jem episodes - which is great if you aren't fussy about it being in English and can play PAL DVDs! Despite the Rhino DVDs finally becoming available, not much else happened until 2011.

2005 -
Kero distributed by Citron Rouge releases the first 22 episodes in French/Pal format in a box set. 2 discs released in Australia by MRA Entertainment.
2006 - A few Jem episodes are released on compilations by Harmony Entertainment in the US. Kero distributed by Citron Rouge releases another box set in French/Pal format (series never to be completed); 2 more discs released in Australia by MRA Entertainment. Company of Kids in The Netherlands releases Truly Outrageous! the movie on DVD (Pal) in English with Dutch subtitles. Truly Outrageous! the movie and a couple other episodes are released on "girl cartoon" compilations by Metrodome in the UK.
2008 - MTC Medianetwork Communication Srl in Italy releases two DVDs, available at small book stands and shops.
2010 -
For the first time ever, the entire Jem series is available for purchase with beautiful new art, by Declic Images distributed by Manga Distribution - dubbed in French (no English option)/Pal format.

In 2005, a new annual, completely fan-run tradition begins in Minneapolis, MN, with Jemcon 2005.

2011- Shout! DVDs and New York Comic Con

Shout! releases the Jem series on DVD. It is available as the complete box set, or in three separate sets of 20+ episodes each. Hub in the US and Teletoon Retro in Canada started airing Jem on TV again, in time slots aimed at attracting older viewers - surely I'm not the only one to have noticed all the car and exercise machine commercials that run during it, am I? The Shout! DVDs were not enhanced at all, and so have a vintage look to them that some find more genuine, others suggest was cheap or lazy. Hey, at least Pizzazz has green hair again! And finally the "lost" Jem episodes with the Stingers would be seen again (in English); for many for the first time in 25 years! Includes a bonus disc of extras, including vintage toy commercials, storyboards and Jem bible excerpts.

After a lot of hype, Hasbro's Jem booth at the
New York Comic Con was revealed on October 13th, 2011, featuring a booth babe in a Jem costume, some vintage dolls and other memorabilia from Hasbro's archives, the Shout! DVD set & T-shirts from WeLoveFine.com. Available to attendees were the following items:

a comic called Unit-E, which featured a mash up of various Hasbro licenses in which Synergy and Jerrica make an appearance, subsequently (and possibly still, as of this writing) available for purchase on Hasbro.com
-a postcard advertising the release of the DVDs,
-a white terry wrist band with the Jem logo,
-an inflatable guitar with the Jem logo,
-small print of Jem in Patrick Nagel style (left)

It was hardly the most exciting news for most Jem fans, who had much higher expectations (New dolls! New cartoon! New holographic projecting earrings that really work! A real pink llama!...). But I'm a glass half-full kinda girl, and I was happy to see anything new, and most importantly the mere fact that Hasbro acknowledged her existence again. Little did most of us suspect the news that was soon to come...

 2012 - Integrity and San Diego Comic Con.

A week or so previous to the event,
Integrity Toys came almost out of nowhere with an announcement that Hollywood Jem, the first Jem doll available in 25 years, would be unveiled and sold at San Diego Comic Con; following that, some would be available at Hasbro's website. Since the convention had been sold out for months previous, the chances of Jem fans being able to attend was slim to nil, so the vast majority went to scalpers. There was no formal announcement for when the dolls would be on the website, but it was of little consequence, as only a small number could have been available for purchase there -the complete run was limited to 500 dolls! And so Jem's rebirth was bittersweet, as several fans were disappointed by the inability to get one for themselves. However, for those lucky enough, she was a real treat. As with the re-airing of the cartoon on Retro cartoon channels, the rebirth of Jem is aimed at adult collectors, and so the quality is much higher than that of a playline doll; the storyline and design kept true to the original concepts. The packaging was also reminiscent of the 80's version and her look combined elements from the cartoon, box art and the old Hasbro dolls. Of course, fans are notoriously difficult to please, and some have cited her "mature" look as a turn off, as well as the high price ($135 US - if you were lucky enough to get one for list price - most people ended up paying at least twice that amount).

There was a Jem postcard at SDCC too, advertising the costumes, the Shout! DVDs and WeLoveFine merchandise.
SDCC 2012, there was an exclusive Jem cover of Haute Doll magazine. Non-convention versions of the magazine did not have Jem on the cover but still had the article about her return inside.
Also debuting at SDCC were Jem costumes that would be available at Spirit Halloween, a seasonal Halloween store. There were licensed baggie costumes and wigs available in adult sizes of Jem, Pizzazz and Synergy, as well as an inflatable pink guitar (not the same as the one sold at NYCC 2011). Sorry about the crummy stalker cel phone pic of their display but I couldn't resist!
In September 2012, at the Fashion Royalty convention, Jemstar earbuds were given away as schwag, and four more dolls were introduced Classic Jem, Jerrica Benton, Rio Pacheco and Synergy, a few days before they became available for preorder through Integrity dealers (October 5, 2012) Jem and Rio sold out swiftly at presale.
In November 2012, Holt Renfrew stores in Canada stocked Jem dolls in *most* -alas, every Holt Renfrew but the one in my own city, argh!- stores. As merchandise sold in Canada must have both of our official languages, the Holt Renfrew boxes came with French/English sleeves that slide over the box, they also came with a clear mylar cover so the doll could be displayed instore.

2013: Integrity keeps on delivering!
2013 is shaping up to be another banner year for Jem and Integrity. In February the Holograms (
Kimber Benton, Aja Leith and Shana Elmsford) were announced and shipped in March. 
The Misfits (Phyllis "Pizzazz" Gabor, Roxanne "Roxy" Pelligrini & Mary "Stormer" Phillips) were announced in April, they in turn shipped in May.
June 5, 2013. Apparently being handled by Hasbro exclusively, they will have a presence at this year's Comic Con, July 18. An exclusive doll, Glitter 'N Gold Jem/Jerrica will be available for sale to attendees, presumably the majority of these will then be scalped on eBay. Glitter 'N Gold Rio Pacheco is also introduced.
July 2013: Broadway Magic (W Club Member doll) announced, The Stingers (Riot, Minx and Rapture) are previewed and ship in late September.

December 2013: The Who is He Kissing Giftset is shipped; Stage Essentials sets are previewed.

2014: Integrity continues; A Jem movie! A Jem comic!
The Countess Du Voisin doll is made available to entice prospective W Club members. Raya and Jetta are announced mid February and shipped in March, along with, surprise! Astral Eldrich who never made it past prototype stage in Hasbro's time.
March 2014: A Jem Movie is announced. 
In late March the In Stiches Pizzazz & Jem set is previewed and shipped to W Club members which become available to the general public on April 4th. 
Clash Montgomery, "Danse" Dvorak, "Video" Montgomery & Regine Cesaire, was announced for sale mid May, 2014. Shipped mid June.
Rockin' Romance Jem is sold at San Diego Comic Con 2014, and shortly after through Hasbro Toy Shop.
October: IDW Publishing announces a new Jem comic book, by writer Kelly Thompson and artist Sophie (formerly Ross) Campbell. Jem begins anew in a contemporary setting with completely revamped character designs and backstory. It is unrelated to the upcoming film. The first issue was available in March 201. 
Techrat is announced as the 4th W Club exclusive doll in November 2014, scheduled to ship mid-June 2015. Two Honda car commercials, featuring Integrity Hollywood Jem doll and Gi Joe airs. 
A December W Club email reveals a small close up of Lindsey Pierce's face, as well as hints of other versions of Jem herself in "fan favourite" fashions coming up for 2015

2015: Integrity's license is extended, comics and movies!
January: The W-Club upgrade doll (the Color Infusion line's Ollie Lawson) looks suspiciously like Kimber's boyfriend Jeff Wright.
Lindsey Pierce is announced as an IT direct doll, available for preorder in mid-March. She sells out in 4 hours!
IDW's Jem Comic #1 is available in March 2015, #2 in April 2015, with more issues to come. 
April: Joecon previews an exclusive Joecon comic book cover featuring Jem & The Holograms with Cold Slither! Alas, there is no story to go with it. Running Press announces a 'retro' Jem book with "Light Up Synergy Earrings"!
May: Jem Comic #3 is released, The Jem movie trailer is previewed.
June: Shopbop announces a Jem "legacy doll"(!); Sephora and Manic Panic will also have licensed cosmetic items available in fall to tie-in with the Jem movie. Anthony Julian is announced, and promptly sells out. San Diego Comic Con's doll is Twilight In Paris (or as us old skool fans know it, Like a Dream) Jem/Jerrica!  Techrat's release date is pushed back to late August.