Nothing gets me motivated more quickly than thinking about getting work done so I can get outside. This site has some awesome mountain bike pictures and videos.
Mountain biking is a kick-ass way to stay in shape, burn off stress, and get out in the woods. Research suggests that light stimulates brain chemicals that improve mood, and for good results, get sunlight exposure first thing in the morning. Phototropism in plants is mirrored in our own evolution.
So if you want to get a change of pace going, consider a change in workout to make your exercise regime more interesting.