I know this may not be an option... but have sex. I'm not kidding...this always works for me. The only times I ever have trouble sleeping is when I have stress. A quick romp or two with my girlfriend before bed always takes care of the problem.
most of the things that have been mentioned here (besides sex ) have alcohol or some other undesired medicine in it. Try some melatonin. It is what your brain produces to tell your body that it is sleep time. You can buy it in any drug store, wal-mart or supermarket. I get my from GNC cause even thought there stuff is more expensive, it is higher grade than anywhere else.
I used to have terrible insomnia -- I'd often have trouble sleeping everynight, and it would take me 3-4 hours to fall asleep even when very tired. I have been able to nearly solve the insomnia fully. There are a few things I've done:
a) Exercise! I can't tell you how important this is, if I go more than 2 days w/out exercising, I'll have sleeping problems again.
b) No caffeine. No coffee, no tea, no soda, limit your chocolate as well. At first, you may find yourself withdrawing from it, or sleepy, but your body compensates for it.
c) Don't take naps. They goof up your circadian rythms.
Beyond that, get yourself on a regular sleeping pattern, and maybe consider meditation to reduce stress (although exercise is effectively proven to be the best stress reliever).