I got Sennheiser HD428 (under $75.00) for around the office, to mute out the AC. Very good isolation for the money, but I can still hear people knock on my door, which is nice. Sound quality is very flat and realistic which I like very much.
My other pair of cheapo cans is the Sony MDR-XB500. They're massive, but like the HD428 are also very comfortable and light. The sound is a completely different story, because the Sony's have a very lively bass enhanced sound. If you like a V-Shaped EQ, boost the bass & treb and drop the mids, and listen to a lot of metal on a MP3 players, these could work very well for you.
