Not sure any have made me feel as rapturous as you suggest, but I've a few that we return to, some every trip.
AP - Sentimental favorite (as you know from a previous post).
Jiko - Never had a bad meal there.
CA Grill Brunch - This is one meal we've truly enjoyed. More relaxing than the testosterone-fueled feeling we get when we eat dinner there, and you get plenty for the $$ (Disney standards, of course).
Il Mulino - Casually upscale setting, good food (small plates, anyone?), nice wine list.
Morimoto Asia - the buri bop is worth going for alone
The Boathouse - fun, airy, solid to very good food
BiCE - Okay, this one is offsite (in fact, located at the Dark Side) but is worth the signature price splurge. Their osso buco is one of the best I've had anywhere. Wine list is superb.
Don't Bother (for us):
Paddlefish - Two visits; two disappointments. Service subpar. Food mediocre (except lobster corn dogs). Signature in name only.
Monsieur Paul - Worst dining experience we've had at Disney. Ambiance was that of Golden Corral (for the record, I like GC fine but no one can successfully argue it has a signature feel); food was lukewarm; service was intermittent. Price for that experience was out of line for what we got.
Stands alone:
Victoria & Albert's - as others have said, it's not really a signature, more of a super signature