My number one is Delamorte Delamore AKA Cemetery Man, though it's not the clear-cut definition of a zombie film. It's really grand--tons and tons of hilarious bits of dialogue, some Evil Dead II-like comedy, obscure philosophy...it's never boring, always strange, and fascinating. Just a brilliant film.
I also would have to say I loved "Shaun of the Dead." Besides being very funny, I found that it was also way scarier than the average zombie film, in part BECAUSE of its humor. You laugh with and at these characters, thinking that this is going to be a comedy, and then they're getting killed in uber-bloody ways and suddenly it's not so funny. The third act is intense as f**k, if you're not the sort of person who laughs at gore, anyway.
Evil Dead II's also gotta be on the list, naturally.
Fido was pretty grand but it didn't hold up the second time in my opinion.
Both Dawn of the Dead films are pretty good, but in different ways. The original's got a dry, dreary charm to it, and an intelligence that the remake lacks. But the remake is just fun to look at, with great cinematography, especially in the beginning (with the car driving around the chaotic neighborhood and what not). I also loved how it used Richard Cheese's cover of Disturbed's "Down With The Sickness."