I've found that reading sci-fi/fantasy before going to sleep helps me transition to sleep mode. I think it's because sci-fi problems are really somebody else's problem, so my brain can let them drop when I put the book down.
I really couldn't agree with this more. Reading before you sleep is so important to getting a good night's rest. Using a physical book or an e-ink screen, anything that doesn't emit light itself.
Seriously, invest $150 into getting a good e-reader, if you don't have one already. It's well worth the sleep benefits, potentially even more than a good mattress (for a programmer, anyway).
One thing I personally found useful was f.lux - an OS X app that changes the temperature of your screen when it gets dark outside. Sounds trivial but makes a huge difference.
