Get on the computer and work on my unpublished website, play memory games or live here at Eden, lol!! If that is not sounding satisfying, I read or watch tv. Sometimes I do crosswords, though. I guess it depends on why I cannot sleep.
I generally tend to either read, or get online. Both of these are bad things for me to do when I can't sleep, though; once I start on either, I'll end up staying up far later than I should. It's better for me to just lay down and try to relax when I can't sleep.