I've played bluegrass guitar (among a couple other instruments) since I was a young teen. I've had a few hobbies since then, but that's the only one that's still strong. Oh, and video games.
Wine (expensive hobby)
Classical music (passive)
Sports (in the gym daily, thinking about picking up kyokushin karate again)
Cooking and dining out
Whisky and cognac
Chess
Electric Bass
Upright Bass
Writing music (I've been dabbling in Dubstep... Using Reason 4...Mwahahaha, I'm totally going to plug my SoundCloud right quick http://soundcloud.com/the-elephant-masquerade )
When I have money, I enjoy working on my car (99 Eclipse N/A). I do all maintenance I can myself.
Listening to music
Hanging with friends.
Driving.
Drinking beer and whiskey, ought to get into homebrewing one of these days
Reading books (sci-fi, fantasy, history, philosophy, classic literature, whatever happens to strike my fancy)
Thinking (this might take up more time than any other hobby...)
Playing bass
Listening to music (of all sorts; right now I'm exploring the vast array of music from all over Africa)
The occasional video/computer games (which is to say, I'll get the itch, and play a lot for a few days or weeks, and then let them gather dust for a while)
Riding my bike
Frequenting museums and gallery shows (good art, interesting people and free booze at show openings!)
Being outside, often acting like I'm still 12 years old (for instance I rediscovered how awesome swings are a few years ago)
Exploring (when I first came here for school I think I spent more time aimlessly wandering around the city than I did on homework)
Open Water Swimming
Just started freediving & underwater photography
Bike riding
Playing piano
Backgammon
Watching films in nice, old, proper cinemas.
Horticulture
Pyrotechnics - I'm licensed in a couple of states and federally. I'm on the Board of the Pyrotechnics Guild International. I build shells, rockets, ground displays and compete nationally. This is a hobby that takes all my time recently (yes... even more than shaving... I post more on the pyrotechnics lists than here... figure that one out)
Cycling (not any more... getting too damned old). Have ridden across the US North to South, the Rockies, and a couple of states.
Shooting pistols and rifles. Compete occasionally but prefer to just go out and play.
Good wines and Scotch
Scuba diving (not any more... no water around here so I have set it aside) - certified with four agencies and have made bubbles around the world. Once discovered a sunken German (WWII) submarine. Saw a mermaid in Cypress. ;-}
Guns
Home Theater
Cars and track days (less so these days)
Hunting
Talking about physics and other scientific stuff with my dad
Working on house projects / remodeling
Ham Radio
Hiking and Climbing
I still collect baseball cards. I'm the guy who's Mom didn't throw out all those old baseball cards. Quote of the Day (Babe Ruth, on baseball “The Only Real Game in the World” I happen to be in total agreement.... Not by any means to demean other sports, as I do enjoy other sports, but rather just my personal feelings on baseball....