I cannot stress how much I agree about exercise. About 6 years ago I started going to the gym regularly* and lifting. That was really one of the best single changes I've made in my life. I feel more energized during the day (no more coffee!) and I feel like my mental acuity is higher. My memory seems better and I'm generally in a much better mood (partly because I look so much more fit!)

* When I say regularly, I mean I went every other day for 6 months without missing a workout. I made it a high priority. After 6 months of that, I felt so guilty if I missed a workout that I've more or less continued that schedule for the last 5.5 years.