Fieldrunners: Hands down, this is one of the best and most polished iPhone games going. If you're a Tower Defense fan, check this out.
Lux: Remember the board game Risk? That's what you have here.
Zombie Attack: Defend your home from roaming undead by setting up turrets and traps.
Hero of Sparta: In this pretty impressive God of War-like action game, some solid hack-and-slashery is going on. My only real complaint is that the frame rate can get a little choppy at times. Still, it's a solild effort that's a lot of fun to take a stab at.
Chocolate Shop Frenzy: Fans of time-management games like Diner Dash need to check this out. In it, you serve chocoholics and play a Bejeweled-style minigame at the same time.
Dropship: This title is a high-style, vector-graphics flight game.
Topple: Playing this Tetris-like game takes a very steady hand. The difference here is that you want to stack your blocks up as high as they will go--and make sure not to tilt your phone too much in the process.
Brothers in Arms--Hour of Heroes: This is an amazing rendition of the World War II shooting title, ported to the iPhone. The controls are surprisingly smooth, proving that you can have a good shooting-game experience on your handset. It's...wait for it...a blast.