I have a variety of card games ... we play them in the infrequent weekend long gatherings my pen and paper group has at my place (normally bank holidays).
First up, Munchkin. Munchkin, and all its sequels, are roleplaying reduced to the absolute basics. Kick open the door, kill the monster, loot the treasure. The aim of the game is to be the first to get to a certain level (normally 10). You get a level by killing a monster (or via a few other cards in the game) .. but because the players are all munchkins, there is plenty of backstabbing along the way.
Munchkin is basic fantasy gaming. In addition you have Star Munchkin (sci fi), Munchkin Fu (HK action movies), Munchkin Bites (horror), Super Munchkin (supers), Munchkin Impossible (a spy one), The Good, The Bad, and the Munchkin (western), Munchkinthulu (Cthulhu munchkin) and the latest I believe is Munchkin Booty (Pirates). As well as these, you have add ons for the different games, and Munchkin Blender, which allows you to mix 2+ sets together. At that point it gets exceptionally silly.
Player 1 - "My half elf, half catgirl yakuza/werewolf attacks the Gazebo with the Boots of Buttkicking and the Chainsaw of Dismemberment Of my Grandfather"
Player 2 - "The Gazebo is actually from another dimension" (Gazebo gets +5 levels and a stylish goatee)
Player 3 - "So is its clone" (add a second Gazebo from another dimension)
Chez Geek: Chez Geek is basically a game set in a shared appartment. The players are the people that live there, and the aim of the game is the first to reach a set number of slack points. That value is determined by the job card the player has .. each is different, and gives a player different free time (actions) and income (cash). The more you have of one, the less you have of the other, generally speaking. Buying stuff gives slack, as does different activities. Some players get bonues to different activities because of who they are (i.e. the Drummer gets +1 to their nookie rolls).
Follow up to this include Chez Greek (At University), Chez Grunt (in the army), Chez Goth (like Chez Geek, but with added Gloom) and Chez Gueverra (slacking revolutionaries).
Another fun game is Illuminati. The players each represent one of the secret masters of the world (or wannabe masters at least) and you build your powerbase by taking over various groups. Groups give power and cash, and the addition of artifacts gives more fun to the game. My group will NEVER let me get the Orbital Mind Control Lasers ever again
My last game, I had the Servents of Cthulhu, who by turn 2 or 3 had turned into the Servents of Zoidberg instead .. woopwoopwoopwoopwoopwoop
Each group has their own victory conditions.
Another fun one is Kung Fu Fighting. Its a fairly straightforward game .. you are the ancient and honourable masters of kung fu, out to prove that your kung fu is the strongest. Kick, punch and trip your way to victory, utilising the stances of the snake style, the tiger style and many others. This game is best played with everyone doing badly dubbed 70s kung fu movie voices.