Cuecat? Though I'm not sure if that ever really got big enough to warrant a spot, but it was a thing for a hot minute.

HomeRF - The wifi contender that was supposed to unify wireless networks across multiple device types.

Tivo - technically still around, but pretty much a zombie version of their former selves. (Maybe make an "I'm not dead yet!" section).

Gateway 2000 PCs -Their support line had a DJ, and they were everywhere until all of a sudden they were nowhere.

Optical Drives

Zip Drives - 100MB on a floppy! OMFG!!!11

Slashdot - Digg and Reddit's funky uncle.