Last year I took up knitting (which I really to get on. All I have to show for that little endeavor is an incredibly long scarf that I haven't been able to wear yet, a few gifts and a basket full or yarn I wish to one day whip up into something glorious.)
I think I would like take on gardening. Aside from all of the hipster-chic, hippie connotations that gardening in the city (of which I do live in, kind of) takes on, it would be a personal challenge to keep something other than myself alive. I was inspired by some of the things I've read and seen over at Homegrown Evolution: Gardening in an Apartment Windowsill, (though I'm not sure I'm ready to take on humanure....) and want to live more sustainablly.