I practice parkour… not very good at it at all, but it’s fun regardless of skill level. I used to do a lot of programming, but I got kind of bored with it. Same with gaming… spent a lot of time playing WoW, some playing Warhammer, and then games like Tron too. Now a lot of my time is spent working, reading, and seeing movies (which is convenient, because I work for a movie theater).
Historical reenacting, firearms, historical-themed video games (think: Victoria and Hearts of Iron), horror and sci fi films/short stories, model railroading, computers.
Playing long and rewarding games (like Zelda, Mario Galaxy, Metroid Prime), riding my bike til the end of the world and practicing Krav-Maga (fun and actually useful martial art)
Well, must of the moves are simple and effective, no mumbo jumbo, the main kick of Krav-Maga is the good old kick to the groin, fine-tunning the moves to be able to use effectively even if you exhausted or caught by surprise that is part of the fun. Although Krav-Maga is brutal and not very artsy, it requires a lot of discipline and will.
Of course there are plenty complex and advanced techniques, as well defense against knives and guns. The physical trainning that is quite demanding, so if you have been sedentary for long, you might struggle at first, but no big deal, nothing you dont get used to by the 2nd month.
An unofficial economic system trainer for the game would make it interesting, especially if you could define what private property, what standard, etc. are (i.e. instead of private property in say, a strict sense, you could make it more Georgian or more Mutualist or whatever).
Hanging out with my girlfriend, power lifting, reading, watching sports (Yankees, Devils, Giants), etc. I used to love playing Halo 2 and 3 for Xbox then my 360 broke and I just stopped playing, I may start again though.