I like card games as much as the next guy, but it seems like half the fun must be in creating the cards and making up the rules. (Okay, maybe that's just one-third of the fun. But still.) If you enjoy creating games as much as playing them, check out 1000 Blank White Cards, a party game in which creating the deck is part of the action. (A sample card is pictured at left: Self Trepanation (lose 2000 points).)
A game of 1000 Blank White Cards, or 1KBWC for short, consists of three general stages (described after the jump...)
1. Deck Creation - in which players create some number of cards, starting with a stack of blanks (up to the eponymous 1000 if you expect to play until next year). Depending on the expected duration of the game, you might create a hundred cards in advance -- or you might start with a handful and make more as you go along. Each card can contain any drawing or text you want -- the card can implement rules (all players must discard a card, for example), give you free turns, add or subtract points, end the game, make the player perform a task, anything you want. Also note that deck creation is explicitly allowed during game play, so this early phase is just about setting up the initial game, which will evolve during play.
2. Game Play - in which players draw five-card hands and play them "on" other players. For example, you might draw the Solar Power card, which simply has an illustration of a Lego man driving a solar-powered buggy -- it does nothing on its own (though you might get creative and combine it with something else -- for example, by creating an "Al Gore" card that grants +50 points for any player with a solar-powered vehicle). Or you might draw the I Have No Arms card, which offers eight points if you pick something up with your teeth. (Note that points are completely arbitrary, though many cards offer plus or minus points for various reasons.) As mentioned above, players are encouraged to create new cards during game play, so if you picked up the Pies card (a picture of three pies), you might create a "+5 points per pie in hand" card and play it. Eventually game play ends when the players decide it's over, or something in the game mechanisms (perhaps a "Game Over" card) declares the end. The player with the most points wins. (Unless the game has been altered, perhaps by a "Lowest Points Wins" card....) You can see the inherent complexity of this Nomic game, in which the game mechanics change during game play.
3. Epilogue - in which the characters decide which of the cards created during the game should be kept for future games. This is purely arbitrary, and offers another way to "win" the game -- by adding your cards to future decks.
History and Further Reading - 1KBWC was invented by Nathan McQuillen, and spread through university towns until it was finally written up in GAMES Magazine and even an edition of Hoyle's Rules of Games. (Read more about the game's history.) Several online lists of cards are available, but beware -- many may be offensive or non-work-safe! Check out: Random Card Server from Boston, Another Random Card Server from Boston, Random Card Server from Seattle, Flickr group. Recommended reading: Bob: 1KBWC in Boston, Wikipedia page on 1KBWC.