I've been sort of collecting them lately. I'm currently playing Dead Nation on PSN. Favorites also include Burn Zombie, Burn and the Zombie Island expansion for Borderlands. Also got Zombie Apocalypse for some 4-player couch co-op action, but hadn't had a chance to try it yet.

I think my recent obsession with Zombie-themed games is because it sort of goes back to the roots of traditional gaming styles. Back in the day if you were fighting a mob of baddies, they didn't fucking hide behind shit or have loads of AI.