Given the fact that you need so many of them 15mm is the perfect scale for Zombie games. Here’s a tutorial on painting them.
Zombie Santa and The Elves of Doom. Nuff said.
Anatoli’s Game Room has a photo tutorial on painting zombies.
Zombie Squad is billed as a “zombie horror survival” RPG. Looks like fun.
Zombology is a free print-and-play card game from Eurydice games. It’s advertised as a 10 minute, semi-coop, card drafting game for 3 – 8 players.