If we are talking about remakes, and Not JUST improved graphics, then;
-Morrowind - (great game, but maybe overhaul the combat)
-Kotor & Kotor II (Better Engine, Better Graphics, Better animations)
-Star Wars Battlefront II (Better Graphics, More Units, Better AI, Better Engine, More compatibility with new systems)
-Star Wars Empire at War (More unit variations, Better Graphics, Smoother gameplay, More factions)
-Medieval Total War 2 (its not so old But I would like to see it on the Shogun 2 Engine because it runs better for me)
-Freelancer (Awesome game but need better graphics, better engine, more ships)
-Fable The Lost Chapters (really just a graphics enhancement would do here, and maybe modding tools, better ones)
-Warhammer 40,000 Dawn of war (all the first ones, you know where you can BUILD A BASE they were awesome and I still play them)
-Command and Conquer Red alert 2 Yuri's Revenge (Bloody awesome RTS, would love to see it with better graphics and maybe more units now)
-KKND2 Crossfire (this was such a great RTS in its time, now I can never even find it)
-Dungeon Keeper (many games TRY to remake this, but they seem to fail at many key points)
-Fallout Tactics (awesome RTS/Tactics game, it would need a more free-form gameplay, like joinable factions etc and better graphics
Thats all I can think of right now, So if there are any Devs out there that need an idea of something to reboot, DO NOT CHANGE THE GAME! just enhance it.