I primarily practice martial arts, I do some cardio, a lot of stretching, and some running. I swim when I can, and I trek on holidays.
I enjoy exercise a lot. Simply put, my reasons for exercising are just that it makes me feel good.
I feel fitter, get less tired, and am able to enjoy Nature's bounty on long treks. I find that a good exercise session either calms me down and generally makes me feel pleasant, or it boosts me up like anything so that I actually behave like I'm on drugs. (I'm being serious - really) I think I'm addicted to it - I find myself craving the 'rush' and get cranky if I don't get any for a few days.