It's rare for me to have a hard time falling asleep now, but I will usually find something "mildly interesting, but somewhat boring" that runs for a long time period on TV and lay down in bed and watch it. I know that won't work for you since you don't have cable though…

It's probably best that you avoid getting on the computer at all when you can't sleep because it's so stimulating and can suck you in. Maybe you would be better off picking up a "mildly interesting, but somewhat boring" book and lay down and read it in the guest bedroom?