Estes 1469 Tandem-X Launch Set
As a kid, I always enjoyed model rocketry. Getting to build something with your dad then launch it in to the sky is hard to beat.
The Estes 1469 Tandem-X Launch Set is a great way to get started. For $30, you get two rockets and a launch system, including platform and electronic starter. I can't wait for my son to be old enough to enjoy this with me, like I did with my dad.