Probably the original Dawn of the Dead for me, there are more stunning movies by this point but I still really like this one, it has held up incredibly well for being so old. I like a lot of the other zombie movies, Night of the Living Dead is really good, Day of the Dead and the remakes are still pretty damn cool. I don't really consider Evil Dead a zombie movie, it is more of a supernatural monster movie but yeah I love those movies too. Walking Dead is the best thing out there currently and I feel I have to mention it since it is about to be back on the air, really excited.
A good question would be favorite zombie video game? I honestly don't think there is a definitive answer, you could say Resident Evil but that hasn't ever been purely about zombies. I really have yet to find a zombie game that has satisfied my need, I thought Dead Island would be the answer but it left me sorely disappointed.