Console: Amstrad GX4000
Discontinued in: ~1990
This epically unheard-of beasty came and went as quickly as you walk from your front door to the mailbox. It's huge, played massive carts and kind of looks like it belongs in a hospital. Even with a version of RoboCop 2 in its library, kids happily ignored it in favor of the SNES and Genesis.
Console: NeoGeo AES
Discontinued in: 2004
Think games are expensive now? Imagine shelling out $200 for games that are now readily available on Wii's Virtual Console. The pricey carts kept it from mainstream success, but certain niches adored the system enough to warrant software support well into 2004. This makes NeoGeo one of the most long-lived systems of all time.
Discontinued in: ~1999
The TG-16 and its manyadditions(like this CD) never took off in the US or Europe, but the Japanese market was much more attentive to NEC's multimedia plight. There are so many revisions and changes to this basic idea - CD-ROM games - that it's no wonder the console failed to find a large audience. The variants also make it tough to pinpoint exactly when this console went belly up.
Discontinued in: ~1999
A handheld TG-16 that was also famous for its TV Tuner, a device that in 1990 was freaking amazing. Watch TV anywhere? What sort of mad sorcery is this?
Console: Game Gear
Discontinued in: 1997
Essentially a portable Master System, Game Gear tried to fend off Game Boy but ultimately faded into nothingness. Partly to blame for its demise were the six AA batteries needed for power that it guzzled like a stretch Hummer with stadium lighting. Strangely enough, it saw a brief resurgence post-2000 through Majesco. The re-issued unit allegedly had a better screen and higher-quality speakers.
Console: Master System II
Discontinued in: 1992
A small re-issue of the original Master System, with no card slot or, oddly enough, reset button. Apparently included Alex Kidd in Miracle World as a pack-in game already programmed into the console. It didn't reignite interest in the Master System, so Sega wisely put its efforts behind the Genesis/Mega Drive.
Console: Super Famicom
Discontinued in: 2000
Easily one of the most revered and popular systems of all time, the SFC/SNES proved Nintendo could lead the market into the next generation and had massively popular games that are still heavily traded on eBay and other markets. While technically slower than the Genesis, its many other advantages (color palette, superior audio, graphics capabilities) helped propel it to an eventual victory.