Well, the PX 100 is open air.

We like the Sennheiser HD 280 Pro headphones, which are sealed and offer good sound isolation. I think they are more comfortable than on ear phones. They cost more ($100 plus shipping at Head Room, but they really are first class phones. Their basic balance is very similar to that of my main speakers. They are also very sensitive and a computer sound card will drive them easily.

http://www.headphone.com/guide/by-ma...hd-280-pro.php