Any of the Romero zombie flicks are awesome, naturally, but the cheesier, more comedy-focused Return of the Living Dead series by Russo is also highly entertaining. The first Return was an absolute classic, and the "send more cops" line was brilliant!
Army of Darkness and The Evil Dead, naturally, are iconic, and for good reasons. There are more classic one-liners in these two flicks than any ten other movies put together.
The 70s flick Zombie, buy Fulci, is a brutal zombie movie with some really groundbreaking and gruesome effects. The eyeball scene is horrible and awesome.
Although not strictly a zombie movie, C.H.U.D was great fun.
The Dead Hate the Living was also pretty fun.
Zombie Nation was one of the worst-reviewed horror movies of all times, but I found it incredibly entertaining. I also ADORE terrible movies, though, so take that with a grain of salt. I own a boxed set of Godzilla DVDs <img src="/ubbthreads/images/graemlins/rolleyes.gif" alt="" />
There are many more I enjoyed, but these are some of my standout faves.
Have I mentioned I really, REALLY like zombie movies????