To the OP -
Head-Fi.org - Headphone forums and reviews for audiophiles is a great place to learn about headphones and HeadRoom at
HeadRoom: Stereo Headphones, Amps & DACs, Wireless, Noise Canceling, Ear Canal, Earbud, Audio Cables & Accessories has a tremendous selection and tons of information and advice as well.
Ear buds offer the best isolation if they fit well. Some people find them uncomfortable to wear for a long time. They're also not as easy to take on/off.
On ear - if you wear glasses the pressure of the on ear may make them uncomfortable.
Over the ear - less of an issue with eyeglasses. They are bigger and thus may not be as portable or 'cool'?
Closed back gives better isolation than open back (but not as good as well sealed earbuds)
I tried an early pair of the Shure earbuds but couldn't get them to stay sealed. I've heard the Etymotic 4s and they sounded great and seemed to fit well.
I love my Grado SR-60s and used to listen to them all the time when working in cubicles. However, they are open back so don't give great isolation and they are on ear so they hurt after a few hours. Grados are still assembled in USA fwiw.
The Sony MDR-V6 are closed back and sound pretty good for the price. They used to be popular among concert tapers as well as the Sennheiser HD 280 pros.
The Sennheiser HD600 were very comfortable (being over the ear) and sounded great, but were harder to drive than most so didn't work as well powered by an ipod. I think the 650 is the current model.
If your son might wear them in a noisy situation and be tempted to crank em to compensate (like mowing the lawn) I'd get a good sealing pair of earbuds. They'll sound good and hopefully he will be less likely to damage his hearing.