It will probably be a lot easier if you give an idea of what games you like.
One thing to keep in mind, if you've ever played a game on your phone and thought, "this would be so much better with a bigger screen", then try that.
Personally, I like playing things like RPGs on my tablet over my phone. Also, some puzzle games are a
lot better on my iPad. I have larger hands, so when I try to play
Puzzlejuice on my phone... it's a real pain in the ass trying to select letters and still control the descending blocks.
What I typically do is keep an eye on
IGN's Wireless Section. They usually post an App Store Update about every weekday, and they include price drops (usually temporary) as well as free games. They usually hit the highlights, but they do sometimes miss a game or two or ignore that the iPad version may be on sale (they'll only list the iPhone version).