Supposedly the happiest and most satisfied people are those who work outside in some form of manual labour. It keeps you fit (one of the most important things for health in body and mind), you are out in the elements (nature woot) and get the sunshine as well as learn to love the bad weather.
For the next 3 months I'm working doing basic garden maintenance with another guy. Got to say I'm already loving it. Very hard work but leaves you pretty satisfied.
Other than that I went mountain biking, just 15 miles, today for the first time in years as I've been at uni/working sundays for the past 3 years so haven't gotten the opportunity. I was feeling pretty down in the morning but after a couple of miles I felt much happier and was really enjoying myself.
Sometimes it can be hard to push yourself to get active but it really really does help. Then when you come home tired (in a good way) and hungry you can eat and computer game for the rest of your free time. Makes a good balance really.