... and someone delete this one, please.
MMCD (the precursor to DVD)
and, soon to be, Blu-Ray (HD-DVD is cheaper and it's already here).
It seems they're the first to come out with the technology, but they never prosper. Kinda like what happens with their WEGAs (I think Tom or Molly talked about that once in a podcast). WEGAs are clearly the de facto standard for HDTVs, but other companies come along and copy Sony's technology and make it cheaper.
P.S. Yeah, MiniDisc belongs somewhere in there; but I don't think anybody really took that one seriously!