A few exercises that I came across have helped me improve my vision. I THINK I came across them at
HowStuffWorks - Learn how Everything Works! but I may be incorrect.
One of them is to exercise your focusing muscles, stick your finger out in front of your face (or some other object) and focus on it, then shift your focus to something in the distance, and then back to your finger, keep repeating this, you can use more than 2 focal points (IE your finger, a chair a 10 feet away, and then the wall 50 feet away). After a while your eye muscles will get sore, this is like working out any other muscle of the body.. which kind of proves it is actually doing something!
Another is to exercise your peripheral vision, to do this you can try and take in as much of the background as possible (even while staring at this screen, try and take in as much detail around you using your peripheral), I also recommend doing this while driving.
And to exercise the peripheral muscles, try and look as far as you can in all directions, keep repeating, you can actually feel the workout this gives to the muscles.
I have been using these exercises and have noticed improvements in my ability to focus on objects quicker as well as notice things in my peripheral more easily, especially while driving (hey it could save a life someday).
And another one that seems to actually be improving my eyesight (ie. not having to need my glasses, the 'blurryness' is getting farther away in my vision), and soon I KNOW (watch 'The Secret'.. use the power of your mind to assist you) I won't need glasses anymore: Close your eyes. Then, take a deep breath and tense the muscles in your body, and then slowly release your breath and at the same time loosen your muscles, this is scientifically proven to relax the muscles in your eyes. I usually do this twice at a time in the morning before I get out of bed, midday, and evening when I get into bed.