Basically all of the donut games look great. Try gold miner and rat on run. Also, nodes of yes, frogatto, the quest rpg, and pandemonium is even superior to playing it on iPhone as is pizza boy. Platformers just work great.
Anything with pixel art should do OK! And some text-heavy games (like word puzzles) can look great, IF the fonts are rendered at native res. But the wasted margin around the sides would still bother me. Go for Universal gamestheyll still run on iPhone/iPod, but will take full advantage of the iPads screen too.
Why your are looking for it? If do you try for example Time Geeks for iPhone in your iPad you probably tell about it's looks great, but it's because you don't see the iPad version. If you have an iPad: Look for iPad games
Now that the iPad in on 4.x, it has the capability to be affected by Retinsizer in the same way as the 960x640 devices. Support is coming in the update. Choices will be 2x+linear filter (what it is by default), 2x no filter (sharp pixel art), and native 960x640 rendering (with black borders, OpenGL games only).
And if there is anyone with experience in emus can you please PM me? I'd like to get a really nice filter compiled for iOS (eg hq2x). 3x point/linear/nearest neighbor scaling: 3x hqx scaling: