Ninja Slash (fun flash Friday). Move left/right/up/down to kill zombies faster and faster.
Skid MK is a fiendishly addictive and entertaining Mario Kart clone which has already taken up far too much of my week. Developers Conix Games also made a top-down zombie shooter in the Robotron tradition called Daytraders of the Dead, which is just about as addictive.
Flash Halloween Friday Fun: Zombie Baseball. John and Sam are the only remaining humans left on Earth due to a horrible virus gone wrong. Sam drops baseballs and you (playing John) hit them into zombies...Rinse and Repeat! The obligatory upgrades and special bats as you increase levels.
Survive the Outbreak: Interactive zombie movie. At certain points of the movie you will be prompted to make a choice. What would you do? You'll most certainly die, but at least you get to come back and try again. *NSFW due to profanity.
ZOMBIEGRINDER! Only a fat man with a shotgun survives the zombie apocalypse in this Abuse-like game with a death metal soundtrack.