I've played both Deus Ex 1 and Grim Fandango recently, and I must say, there is NOTHING wrong with them even after a decade and more since they were released. They are still great gaming experiences, even with the outdated graphics(and that's pretty much the only thing that feels outdated about them). Even better is they run without problems on modern rigs (and a lot of old games don't)
What I'd love to see a remake of is Thief 1 and 2. Some current graphics and audio technology, and they would be hits again. I'd even settle for a patch to make them work on modern PCs.
A high resolution patch for Diablo 2, and I swear I'd be all over that game again (until D3 comes along, but since we're on BlizzTime, that might be a while). It's still the best game in it's class despite numerous newer attempts at the genre. Titan Quest, Deathspank, Torchlight, all games that tried to cash in on the absence of a Diablo 3, but none quite managed.
Max Payne 1 would be nice, I can't get it to run on any of the PCs in my house, and it's a veritable timeline here (starting with a Pentium MMX sporting a whopping 200mhz processor, going through the end days of single core, all the way up to my current gaming rig)
I would also like a remake of the Starcraft 1 campaign (I know there are maps for SC2 already with the first Terran and Zerg campaigns, and they are very well done, but I want the whole thing). I've tried playing it after finishing SC2's campaign, just for the story, but man was the gameplay horribly outdated after playing 2. Just the pathfinding made me want to eat my mouse, and that's not even the worst of it.