I'm a massive fan of the tile game Carcassonne. It's simple and intuitive to grasp the basic rules, it doesn't take hours to play, it's strategic, and it's hard to know who's won until the very end. If you've never heard of it then do take a look (or come round to ours for a game). The iPhone App has now been released, and it's phenomenal. The gameplay is beautiful and addictive without quite replacing the joy of the actual game. I'm aware that there's countless "extensions" to the game, so it grows as you do. Take a look!