A good portion of the apps I've downloaded for my iPhone are ones with "zombie" in the title. That should probably come as no surprise.
Zombie Smash is pretty good, the physics of tossing around these zombies is a lot of fun (inflicting various gravity levels is possible too).
There's a wide range of upgradable weapons you can use to defend your house from the horde, like rocks, grenades, windmill blades, shotguns, meteors and more.
I finished the game on the normal skill mode, and let me tell you, it gets pretty frantic in the later levels. You'll be giving your fingers a workout, flicking away zombies as fast as you can, it's a real finger zinger.