age of empires 2, goes to 1024x768 even though it was made 4 years ago.
but if you mean a constant resolution that cant go lower, there is civilization III, 1024x768 required to play. 8 directions of smooth animation for each unit, with many types of units.
But both those games are RTS - ie the units and stuff are all really small on screen, (and so taking up not much memory) - therefore it's no problem to run at high res. If I scaled all my sprites down that small, I could run at high res like that too. But I am dealing with animated sprites that, in some instances, fill a good part of the screen. Notice I specified, "decent-sized sprites with a decent amount of animation".
Don't get me wrong, I would be happy to do as Wendel does and make 1024x768 my "standard" res, in fact, it would look great - but to do that, it would need at least a 64Mb graphics card to store all the animation in - preferably 128MB! And it would quadruple the download size.