I walk to the gym. It gets me outside, in the light, and I stay longer because it took 20minutes to get there instead of 5.
Also make yourself a really good working out playlist or cd, full of happy, up-beat music that makes you want to sweat. "Die Another Day" by Madonna always makes me push myself.
Oh and try downloading some episodes of Biggest Loser to your iPod, or watching it before you go. Watching people, in much worse shape than I am, work out for seven hours a day helps me get through my two hours. If they can do it, I can!