Actually, I'm just surprised that no one has mentioned DVHS
I remember the first time I saw a prototype DVHS HD deck at CES - I drooled and had to have it, but it was too expensive then. Then D-Theater came out and the decks were "only" $900. I was thrilled.
But of course, the "convenience factor" was never there for a generation that was accustomed to CDs and DVDs. I didn't mind the lack of instant direct-access on the tapes, since the PQ was so gorgeous - but nevertheless was happy to see the arrival of HD DVD/BR.
I still have about 15 boxes of blank tapes, which I use to archive my HD movies. I can even use my DVHS deck as a "transport" for my AVC satellite recordings which are decoded and played back by my HTPC.
Truly was a great product that just shined for a brief moment between two other great products.
Other greats I miss are the Radio Shack Color Computer, the Commodore Amiga, DVD-A and DAT. The ones I don't miss much are the Apple IIc, IBM PS2, Betamax and SACD.