The major difference between childhood and adulthood? Childhood was a lot more fun and cost a lot less. Tap into that kind of fun with a homemade scavenger hunt. Keep them guessing by hiding clever, handmade notes around the house. Watch them have a blast as they chase down their gift: the sofa, some friends, and a movie.
Set them up with a Google reader account and put together a list of their favorite sites and blogs that you know they'll love. Not only does this show someone you care, but that you really know them too.