I work with an internist who likes to use Melatonin but more for cancer prevention/treatment (not in place of chemo/xrt). She often refers to an article published by Life Extension in 2004 (
http://www.lef.org/magazine/mag2004/...latonin_01.htm). Melatonin has traditionally not done very well as a sleeping aid but may produce better sleep once a person falls asleep. It does not make most people feel sleepy therefore if falling asleep is your problem it is probably not the best bet. We usually recommend benedryl for that but also look at whether a person is having trouble "turning their mind off" too. Our social worker provides great techniques for helping quiet the mind.
If you read the article linked here please do so with the mindset that this is early research with limited application to humans (in research). There are more examples of research with melatonin and cancer (see pubmed) but it is not widely used due to limited research. Life Extension does sell supplements therefore I do not use them as a sole source for information because of the conflict of interest they have with product sales.