I'd say Sonic the Hedghog 1, 2, 3, Sonic and Knuckles, and CD…
But then you realize how butchered and retarded it'd be after it's done, and you just kinda back off. Maybe if Sega and Sonic Team didn't handle it...
Maybe the original Duke Nukem? Except Forever is taking forever...
Duck Hunt might be nice as a mini-game...
The only thing I can really think of isn't very old, so unless there's a 10 years since release minimum for it to be classic, I'm going with Halo 1 and 2. Halo 1 is a true classic, and I'd love to see Halo 1 and 2 bundled together with improved graphics, and hey, maybe Halo 2 might actually be as fun to play if they went back and tweaked it? As it is, I'll play Halo 1 and 3, but won't touch 2 now that I don't have to, and let's face it, it's time for a graphical upgrade.
Unfortunately, as with all remakes, bad changes will be made, and the creators working on it will always say "it's for the better", but it doesn't change the fact that you'll like it better in it's original form. In a way, all these remakes would be nice, but I think after they arrived, we'd cry and then ask why, oh why, did they ever think a remake would be a good idea?