Sorry... I'm not going to make my three year old clearly write out his Christmas list. The biggest problem I have with this is the expectation of the child that they will then receive everything on their list. My dad did that with me one year, told me to write down everything I wanted. I wrongly thought I was going to get everything I wanted. It led to disappointment on Christmas, though I tried hard not to show it. Granted, it only took one Christmas to learn that, but I like the surprise, the mystery. And if you do this, let your child know please, that you will use it for ideas, but will not buy everything on it.
I use the power of Observation, reviews for children that seem into the same stuff as him, and certainly shoutouts throughout the year.
I also take him through the toy store and we play our way through. I watch for items that hold his interest, that are educational, athletic, or just plain old fun. I refuse to buy him something every trip, but I let him know that I'll have a word with Santa.
This year he's getting a Innotab 2 based on his love for my Xoom, and his outgrowing his Leaptop.