I’ve played a lot of iPhone games.
If you like old-school RPGs, I can highly recommend The Quest and its expansions.
I also like the pinball series from Gameprom (The Deep, Wild West, Jungle Style), with The Deep being the best of the lot.
Civilization Revolutions is worth a few bucks.
My advice: subscribe to the Touch Arcade RSS feed. They preview and review almost every game, and always post when games drop prices or go free for a limited time.
I will third Soosiz, which is an extremely fun platformer (and really nice to look at too).
The EA Sports games have some flaws, but overall are VERY well done. Especially Tiger Woods PGA Tour, which looks like a PSP game, and the touch screen controls are very good…it feels natural on the iPhone. The only real downside is once you learn what you’re doing, it’s pretty easy to shoot -50 or better in every tournament.
Rolando and Rolando 2 are exceptionally good games too.
I like Need for Speed Underground and, of course, Doodle Jump as well.
Frankly, I think the iPhone/iPod touch are really good gaming platforms.
I haven’t paid for an app yet since all of the free apps keep me busy. www.freeappaday.com, www.freeappcalendar.com and Openfeint’s standalone Iphone app all work with publishers to make one paid game free each day for one day only. The quality of these games varies drastically, but there have been some great games released for free.
I haven’t bought many games either. I really only play Angry Birds and Words With Friends.