Starr,
I live in the UK and I recently purchased melatonin from this web-site
http://www.biovea.net/
I have used melatonin for years, and although it can help, there are two main side-effects. First, it makes me dream a lot, but this is okay so long as the dreams are pleasant. Second, it can result in "rebound insomnia", by which I mean that the insomnia returns the next night (unless I take something). How bad this is depends a lot on how much melatonin I took the night before. In general, I find that it is better to stick to rather low doses of melatonin (about 1mg) so as to minimise any rebound insomnia. Unfortunately, lower doses are less effective at putting me to sleep.
Over the years, I have tried a variety of prescription and non-prescription pharmacological methods. This is an entertaining piece about some of the non-prescription drugs:
"To Sleep: Perchance To Take Lots of Pills. Testing over-the-counter sleep aids, herbal and non."
http://www.slate.com/id/2062791/
For chronic insomnia, I recommend not taking the same pills two nights in a row. I find that varying the drugs varies the side effects, and reduces the amount of tolerance.
Someone else mentioned eating turkey. The theory behind this is that turkey contains the amino acid tryptophan, which your body converts into serotonin and/or melatonin. You can find out more about this on wikipedia
http://en.wikipedia.org/wiki/Tryptophan
You can find tryptophan and/or 5-Hydroxytryptophan (5-HTP) for sale at some heath food stores/ web-sites and/ or e-bay.
Another informative web-site:
"BBC: Science & Nature - How to sleep better"
http://www.bbc.co.uk/sn/tvradio/programmes/sleep/
Finally, what has been most helpful in reducing my insomnia was changing my life-style. In particular, I now work part-time, during the afternoons and evenings. The job involves very little interaction with other people and is not very stressful. The main down-side to this is my annual salary is now about one-third of what it was two years ago. I make just enough money to get by, but that is about it. C'est la vie.
Sweet dreams.