Games of all sorts are my most constant hobby - board games (especially historical wargames), card games (Magic, Poker, etc.), and video games (mostly non-MMO RPG's). I shift between genres throughout the year - this time of the year tends to be videogaming season for some reason. I just picked up Desktop Dungeons yesterday and am having fun with that - sort of a bizarre, roguelike cross between Diablo and Minesweeper. Overall favorite games... Advanced Squad Leader (board, a hobby unto itself), Here I Stand (board, Wars of the Reformation), Magic (card), Persona 3 and 4 (video), and FTL (video).
Like several other folks above, I used to dabble in a lot more hobbies before I had kids. Serious interests at various times of my life include rowing, backpacking, cooking, pipe making, computer networking, security, and programming, and Legos. My "reading" is usually studying mathematics and working problems - I'm a HS math teacher by trade, and like to work on university-level material to keep from getting rusty. If I have some time off, I'll probably read some history. I started building a model ship recently and will probably keep that up over the winter.
It's not surprising to me to see a model railroaders (or admirers) here - it's a very pipe-smoker-y hobby. I've always loved model trains, but live in a relatively small place in the city and can't spare permanent space for a layout. I know I could make something in N scale work, but a layout that small just doesn't grab me. And besides, assembling any kind of decent layout requires more time than I'm willing to invest right now. However, I do bust out big, standard gauge trains (reproductions, not originals) to set up a Christmas layout every year - at about 6' by 12', it's about 1/3 of our living room. For non-RR'ers, standard gauge is about double the length and width of O scale - they're huge! My kids love to see the trains come out every year, and my wife loves to see them put away so she can have her room back.
We just laid out the snow and the track this past weekend, and now my kids will get to work decorating it with Lego buildings. I'm super-psyched... playing with trains is the best part of the holidays for me.