If you like constantly-changing rules without the physical effort... try
Fluxx. I'd been playing the free PalmOS version, and finally purchased the actual card game (which is a later ruleset). Lots of fun.
There's also the Mad Magazine Game (any rule is subject to a majority vote; we once voted that 5 was an even number to prevent someone from winning), but that is out of print. I got it on eBay.
Or, if you are completely out there, go for
1000 Blank White Cards, the official card game of the Discordians.