Recently I've been playing around with binaural and isochronic beat meditation. It's interesting stuff for many reasons, but one of the most prominent effects is that of Delta wave beats. Turn those on and I'm out like a light in a matter of minutes, no matter how awake I was before. I highly recommend it to the insomniacs.
There's a free program called Sbagen (available
here) if you're interested. Load it, put on a pair of headphones/ear buds (you must use some sort of headphone for binaural beats to work, because the effect is created by having two different sounds in each ear), and turn on the basic delta wave. There's a ton of free stuff out there relating to binaural beats, as well as a pay program call iDoser. Less stuff on isochronic beats (which are similar, but different), but a few good sites if you poke around.