I've been looking for a game to amuse myself (and others) with that's a bit more complex and interesting than the standard fare. My current investigations have led me towards the likes of Nomic, Double Fanucci and Mornington Crescent.
Double Fanucci is a card game from the Zork series of games. As things currently stand, Double Fanucci is thoroughly unplayable because I neither have a deck of Double Fanucci cards nor do I (or anyone else) have any idea what the rules of Double Fanucci are. Some information about the game can be found at wikipedia, Encyclopedia Frobozzica and Do-It-Yourself Double Fanucci. If I could manage to get a Double Fanucci deck, it might be interesting to try to construct rules but, until then, there's not much to be done with regards to Double Fanucci.
Mornington Crescent is a game devised by the BBC radio show I'm Sorry I haven't a Clue. The game is either easy or hard, depending on whether you get what's going on or not. The object is fairly simple: be the first to get Mornington Crescent station. Mornington Crescent is a thoroughly playable game, as long as you have some creativity, a sense of humor and know how the game works. In order to learn a bit about the game, take a look at Mornington Crescent Illustrated with Expert Play. Once you give up trying to figure out what's going on, take a look at what wikipedia has to say about the game (bit of a spoiler). This is a game that I should like to find opportunity to play someday despite knowing the trick behind the game.
Nomic is the most playable of the three, being completely real and having clear, well-defined rules. The interesting bit about Nomic is that the rules are modifiable during the course of play. The plastic nature of the rules is the interesting feature of the game and makes for very open-ended game play. To get started, take a look at the inventor's Nomic page and his description of Nomic (including the initial rules). Also, Nomic is pretty popular so you can easily find plenty more info on the rest of the web. Nomic, being thoroughly playable, is something that I hope to convince some people to join me in playing sometime in the near future.