Sleep has never been a strong point for me, so I am always on the lookout for things that help with my pillow time. One of the ones I just found out about was what I would call "low dose melatonin therapy". I was actually biased against melatonin, because I had taken 1 and 3 mg tablets before sleep before and woke up the next morning almost feeling like I had a hangover. And I found out it was not just me: the researcher actually talk about this "hangover effect".
However, I came across an MIT article that explained the problem: I was taking WAY too much melatonin.  I would never take steroid levels of testosterone in my HRT program, but that is exactly what I had done with melatonin. I will go into this a bit more later, but once I started taking around 250 mcg (micrograms) of melatonin - a much more reasonable dose - I woke up feeling much better upon waking. If fact, low dose melatonin has been a huge help in this area and the studies show that it can defnitely be a help for some men. Again, taking 3 mg is so much that that is the equivalent to taking steroid dosages of testosterone. The typical 3 mg tablets that you still see sold in stores are about ten times what you need to take!
Now you have to realize that I am a good candidate for melatonin therapy because of my age. Melatonin levels fall off rapidly with aging and many experts believe that that is part of the reason sleep efficiency, quality and duration drop off as we grow older. I also stay up staring into a computer or TV screen many nights of the week, which hammers melatonin.
Therefore, if you are over ~50, you can consider trying melatonin for a few days and see if it helps. I know that, for me anyway, the results were dramatic. (Always talk to your doctor first if you are on any medications or have a medical condition.)
So why did this MIT article state that 300 mcg (micrograms) was the right dosage level? The writers explained that this was a "physiological" dose, which means that it would simply raise your plasma melatonin to, at most, youthful levels. And this makes sense, because I have read that your pineal gland secretes about 500-800 mcg daily in one's prime. This drops off rapidly in middle age and by age sixty, you are likely making less than half of what you once did. In fact, one study showed that from age 29 to 60, subjects experienced a drop of about two thirds in their melatonin levels. Ouch! 
Therefore, a dose of 300 mcg is very reasonable if you but into a "replacement philosophy" as I do and merely represents the amount that needs to be replaced in order to restore youthful levels. Studies have even verified that 300 mcg does indeed raise plasma melatonin levels to expected values. This built on previous study work that showed similar results, i.e. that physiological dosages (300 mcg) of melatonin could improve sleep without causing any "hangover effect." 
CAUTION: If you have Restless Leg Syndrome, talk to your doctor. There is some evidence that melatonin may worsen this condition.  Melatonin also can interact with some medications and some say that melatonin may cause issues with certain autoimmune diseases and Parkinson's Disease. (The problem is that rarely is that most studies do not look at low dose melatonin, so the issue may not be with melatonin but with excessive levels being ingested. Talk to your doc though.)
So just what can low dose melatonin do for you? For starters, it often decreases the time that it takes you to fall asleep - melatonin is proven to help many men with insomnia - and also the number of awakenings and movements during sleep.  However, it also appears to have superpowers and appears to actually prevent the tangles of Alzheimer's. In addition, there is preliminary evidence that it likely helps with some cancers as well as heart disease, bipolar disorder, reflux (GERD), memory, migraines and certain types of depression.
In addition, I think that getting good quality sleep (and of sufficient duration) can really help many men with adrenal fatigue. See my link on The Basics of Adrenal Fatigue for more information, but a lot of issues in this area and undoubtedly sleep-related. How many men would have had adrenal fatigue if they were getting 8 hours of quality sleep??
One concern that men may have is that taking melatonin will shut down their pineal gland. This is a valid concern, because some glands will atrophy, such as the testes when men are given testosterone. However, still other glands, such as the thyroid, do not usually show signs of a shutdown when replacement hormones are given. As far as I know, there is no evidence that low dosage, replacement levels of melatonin shut down the pineal gland. Furthermore, I called the Life Extension Foundation and they verified that they have seen no shrinkage or signs of this issue as well. Of course, do your own research and talk to your doc: I am just reporting what I have heard.
CAN'T SLEEP? DISRUPTED SLEEP?Finally, let me mention a very interesting study that showed that giving a combination of melatonin, zinc and magnesium was a huge help to insomniac patients. Now the dose of melatonin in this study was rather large: 5 mg. However, the dosages of magnesium and zince, 225 mg and 11.25 mg, respectively were much more reasonable and represent 77% and 53% of an adult male's RDA. All three of these are well-known for improving sleep and various combinations of them have helped men on the Peak Testosterone Forum. The above study showed that this was a powerful combination: time to fall asleep, duration of sleep and alertness the next day were all greatly improved.  Again, I would not take this large dosage of melatonin but try low dose instead along with zinc and magnesium. (Make sure you get absorbable forms.) (If you are not over 50, then you may want to try just the magnesium and zinc: you should not need melatonin.) ARE YOU UNDER 50? If you are less than 50 years old, then I would just stick to the zinc and magnesium. These can really improve the quality of your sleep and our soils are notoriously magnesium-depleted due to "soil erosion."
How NOT To Use Melatonin:
A 2002 study showed us what you shouldn't do. They took young people (average age of 23.4 years) at the peak of their melatonin levels and then gave them a "steroid" level dose of 3 grams per day. This is about ten times their physiological level and, of course, produced nasty results: decreased fertility parameters and lowered estradiol levels.  The authors wrote that "our preliminary observations suggest that long-term melatonin administration is associated with decreased semen quality in a number of healthy men, probably through the inhibition of aromatase at the testicular level.." Of course, many men want to lower estradiol levels, but the point is that horse doses of melatonin produce strange and unpredictable effects.
1) http://web.mit.edu/newsoffice/2001/melatonin-1017.html, "Scientists pinpoint dosage of melatonin for insomnia", by Deborah Halber, News Office
2) Lancet, 1995 Dec 2, 346(8988):1491, "Improvement of sleep quality by melatonin"
5) J Am Geriatr Soc, 2011, 59(1):82-90, "The Effect of Melatonin, Magnesium, and Zinc on Primary Insomnia in Long-term Care Facility Residents in Italy: A Double-blind, Placebo-controlled Clinical Trial"
6) http://onlinelibrary.wiley.com/doi/10.1002/j.1939-4640.2002.tb02281.x/pdf, Journal of Andrology, 23(4), July/August 2002, "Melatonin Administration Alters Semen Quality in Healthy Men"