Two things I haven't seen mentioned yet:
I use a Cyborg RAT 7 mouse. It has a two-way adjustable thumb rest, adjustable palm rest (which I removed completely) and interchangeable pinky rests. You can also adjust its weight. I set the sensitivity very high to minimize the amount I have to move it. There's a button on the side you can hold down to drop down the dpi for precise movements, too.
Exercise has been mentioned, but I specifically suggest martial arts. Within a month of training twice weekly I could notice a difference. My posture is better in general. My muscles are more toned. I'm more aware of my body mechanics. And, it doesn't feel like I'm exercising... it feels like I'm doing something fun and happen to get exercise along the way.
I believe that practicing martial arts will strengthen your bones, tendons and ligaments in addition to muscles. Also, punching drills will teach you to keep your wrists straight very quickly. You'll be around people who understand body mechanics very well and who can give you good advice on keeping in good shape.
Shop around to find a school that suits you. Look for someplace that teaches a wide variety of techniques and will work every muscle in your body. Avoid places that give black belts to children. Avoid schools that require to you sign a long term contract. Hopefully you can find a passionate teacher with more than a few geeks in the classes. Bullshido is a good place to go to get expert opinions on the schools you check out.
The school I train at teaches a type of Kajukenbo. They cover a huge variety of practical techniques. The head teacher is an MD PhD student and most of the students are geeks... seriously, like playing D&D and going to renaissance fairs. It's the best thing I've done for my body since becoming a full time developer, and has been good for my social life to boot.