Has there ever been a really, truly successful add-on?
I can think of a fair few that weren't particularly successful (well, in the gaming sphere at least): Mega CD, Sega 32X, N64DD (was pretty much abandoned never released properly) - not to mention the tons of gimmicky peripherals like the nintendo power glove.

Originally Posted by
Blue Jedi
The Blue rays can hold alot more than a HD DVD and some of the new ones can even hold 500 gig and over double that.
I think you mean 50 gig. HD-DVD can't hold quite that much, but isn't leagues behind.