I have an 8" dobsonian that I'm really happy with. I found it on craigslist for $75 that was only used once and then stored away in a closet. I just bought a few new eye pieces for it and it was good to go.
I'm very pleased with it. You can see Jupiters color bands and 4-5 moons, Saturn and its rings and moons, Mars polar ice caps, moon craters.. Orion nebula is also one of my favorites to see. Also lots of star clusters and double stars etc.
Its great for taking out in the yard or driveway to star gaze. But, not as easy to trasport as others due to size.
Get a good star chart for him also. That teaches you a lot about how to find stars in the sky, and the names of those stars.
Also, there is a program called stellarium which is great to find out where the planets and stars will be in the sky at what time.