He loves Harry Potter? Say no more. I give you Alivan's Magic Wands:
http://www.alivans.com/welcome.htm
But if you don't want to wait for it to be shipped, go find some sort of twig and stick it in a fancy-looking box.
Or, you could get the 2007 Harry Potter calendar I saw at Borders yesterday. It's really hard to go wrong when you know the guy is really into Harry Potter.