I didn't read thru the whole thread, but here's some of the things that helped me a lot. Sorry if they've already been mentioned.
1) I noticed a big difference in my sleeping after getting a white noise machine. I just can't stand silence, and the low hum of one of these things is really calming. Kindof like how some mothers will put their babies on top of a dryer to get them to sleep. My machine has specific sounds, not generic white noise: rainfall, beach, creek, etc.
Here's a common white noise machine. Mine was a little more expensive.
http://www.acousticalsurfaces.com/white_noise/white_noise.htm
2) I cut caffeine out of my diet for a totally unrelated reason, but I noticed it improved my sleeping a lot. And when I say cut out caffeine, I mean i really cut it out: you'd be surprised how many products have caffeine in them. Including chocolate.
3) I saw somebody mention Yoga before. I think this is really good as it involves deep breathing techniques. Once you learn how to do it well it can really lower your heart-rate, and calm you down.
4) Another thing I don't think people have mentioned is to create a good sleeping environment. By this, I mean having a room that isn't scattered with your papers and books, and all the stuff that worries you. I know it can be hard to keep school material out of your room (I can't), but if you're lucky enough to have an extra room in your apartment (or whatever) you should keep study and sleep separate.