There's an allergy pill specifically for nighttime, which helps you get more drowsy. It's nonaddictive, and it's a small effect (it won't knock you out for you), but it seems to help if you're -trying- to sleep.

Mental work is good. Reading, particularly something that requires thought about the subject (articles/books, not twitter/forums/etc. which has instant feed to keep people awake, and junkfood style writings), does a good job. I've been using Hitchhiker's Guide for that. Doing some form of work helps, too.

Unless the game takes a lot of brain work, avoiding games is a good idea. Same with most television, though a relative of mine often uses things like Star Trek (good shows, but not usually high-action or the like) or Ken Burns (awesome documentaries, but also on a slower pace) on low volume.

Best thing in my experience, though, is "meditating"/relaxing. Avoiding thought about things I still have to do or want to do. Usually by paying attention to the senses more.