number 1 app: ocarina. If you have ever played zelda in your life you will be in love.
Also, ichalky is a cheap, fun, simple, (pointless) app. entertaining and well done.
I bought a few games (monkeyball, enigmo, and cro-mag) which are decent, but i don't really find myself playing games on my iphone very often and there are plenty of great free ones (LUX TOUCH!! if u like risk go for it)
Those 5 are the only apps i have bought which are still in the app store (hellooo netshare! )
But really just go for the free apps. About 90% of my apps (if not more) are free and work wonderfully.