Dead Ahead is a game released by Chillingo a few weeks ago, and it's been huge in the App Store charts lately. It's an endless running game where you're actually on a moped (or, later, a motorcycle), racing through a zombie-ridden apocalypse. The game's controls are excellently simple (you move your finger up and down the screen to steer, and then there are two buttons to race forward or shoot backwards), but the biggest draw here is the game's aesthetic, which uses a very stylistic look to add a little bit of whimsy to a pretty spooky zombie setting.
The game is relatively gory, as the zombies are you can either be crashed into cars (or shot apart) in very bloody ways. But for all of the gore, the zombies are also cool, and the various types you'll encounter (including big, hulking zombie bosses) mix up the gameplay quite a bit. As you drive along, you'll pick up coins and earn points, which then let you upgrade your bike, your gun, or unlock various powerups and other fun tweaks.
Dead Ahead is a great title -- it's an endless runner and doesn't really break open the conventions of the genre, but it does perform its few features very well. You can download the game right now for free, and (not surprisingly) there are plenty of in-app purchases to make if you so choose.