This deal has ended.
Amazon now has the Sony Sony MDR-NC6 Noise Cancelling Headphones for $28.99, the lowest price yet. (Circuit City and BestBuy are $49.99, Office Depot is $59.99, all before shipping / tax.) The switchable noise-cancelling function cuts outside noise by up to 70% and runs for 30 hours on a single AAA battery. Shipping is free and there is no sales tax (except KS, ND, WA).