A recent discussion with mouser about the need for more games that focus on hillarity over skill brought it to my attention that there has been very little mention here of one of my all time favorite games -- Kingdom of Loathing
The Kingdom of Loathing is a web based role playing game. The gameplay is primarily single player, as your character proceeds to acquire equipment, food, booze, and meat (the game's currency) as means to progress on various quests. In that regard, it's pretty standard as an RPG. Where it's truly uncommon is its character -- from the character classes to the areas to the enemies, everything is an extremely absurd parody of something. It's funny, irreverent and generally fun.
There are also some multiplayer aspects to it, as you'd expect from an online game. The economy is purely player driven, most items in the game able to be bought and sold player to player. It features a chat where players can communicate in real time, clans for players to team together to help one another out and some simple player versus player mechanics.
Whether you just sit back, relax and play it casually or delve deeper into the economy or making faster, more effecient "ascensions", there's plenty to do. New items are added constantly and new quests and areas are added every now and then as well. I've been playing KoL for a little over two years now and am still amused enough by it to continue playing for years to come. If you do sign up, look up "Terrae", that's me!