I'm a big fan of Looney Labs, having spent many hours playing Fluxx and Zombie Fluxx with friends and family. If you aren't familiar with these games, here's the official description:
The card game with ever changing rules! It starts out simple, with just the Basic Rule card: Draw one card and play one card during each player's turn. But New Rule cards quickly make things chaotic.
Even the object of the game will often change as you play, as players swap out one Goal card for another. Can you get the Rocket to the Moon before someone changes the goal to Death by Chocolate?
And then the Zombie edition changes it up a bit:
Welcome to the dark side of Fluxx, the card game of ever-changing rules! Zombie Fluxx takes the award-winning card game Fluxx and cranks up the fun with a Zombie uprising. The Zombies arrive in the form of a new type of card, called the Creeper, which hangs around in front of you, preventing you from winning.
The good news is, the Keepers include a Shotgun and a Chainsaw and various other things you can use as weapons against the Zombies. Plus you've got Sandwiches and Coffee and a couple of Friends to help you win. The bad news is, if your Friends become Zombies, you'll have to destroy them!
You can see a Creeper card from the Cthulhu edition above, based on Him Who Is Not To Be Named. Something tells me the Shotgun and Chainsaw from the Zombie edition won't be nearly as effective against the Old Ones.
Also, someone is beginning a Kickstarter campaign to develop a Cthulhu/Monopoly mash-up boardgame in which you destroy the neighborhood instead of building it up. You can read more about The Doom That Came To Atlantic City here. Sounds like fun for Lovecraft fans and Monopoly haters alike.