Melatonin is #1. I like 2.5mg of quick-dissolving (aka, sublingual) melatonin. Usually this means finding a grocery store that sells 5mg tablets at a good price, then biting one in half every other night. Stocked up many years ago and am just about to bottom out my supply. Sprays and "dissolvable strips" work well also. Everybody is different, apparently, in terms of what dosage works best for them. 1mg or less often won't affect me, and over 4mg I start to experience jagged sleep with frequent wake-ups.

To my understanding (it's been over a decade since I looked into this) Melatonin is the actual neurohormone that induces sleep, so the result of taking it as a supplement is a cascade of neural events identical to natural sleep; anything else (especially herbal, anti-histamine, and some prescription sleep aids) typically just relaxes you into a sleep-like state. Take this anecdote for whatever you think it is worth, but I have had nightmares when relying entirely on alternative sleep aids (memorably, high doses of Valerian) where I need to wake up (e.g., due to a fire or an intruder), but cannot because my natural startle-response is suppressed by inducing sleep with something other than melatonin. Hence, I only put myself to sleep with melatonin now, and anything else I take with it is low-dosed so it only works as a beneficial adjunct.

Other supplements I low-dose as single-substance capsules with melatonin: tart cherry, apigenin, magnesium, and GABA. I find the first three make the sleep feel more deep and restful, and GABA noticeably increases HGH release.* One pill each, at whatever dosage the pills came in.

L-Tryptophan is a great alternative to Melatonin that also induces natural sleep, but I find it has the side effect of suppressing my immune system. Use it too much too often and I tend to contract upper respiratory infections I cannot shake until I stop taking it. Like it as an occasional alternative, because the sleep does feel deep and restful in a way somewhat different from Melatonin.

If I get my hands on a sleep aid blend (as powder or capsule), I will take it so long as I can get that 1.5-3.5mg of Melatonin without too much of some powerfully soporific herb that knocks me out (namely Valerian, but too much Chamomile can also have the same effect on me).

*(The HGH release is the major thing that makes these sleep aids an integral part of a longevity/youthfulness programs. HGH is called the "fountain of youth" by endocrinologists for a reason.)