My Vote is AKG K271 Studio
I bought my AKG K271 Studio cans specifically for work.
Very good isolation, extremely comfortable, surprisingly light weight, not fatiguing, and right at $200 with shipping. Also they mute when you take them off, which is very nice in an office environment when someone walks up to your desk.
Also they are impressively accurate and revealing. I came from Grado's and feel they make an excellent addition to a set of Grado's for home use. Sound to the Grado's is comparable (considering the fact they are closed and Grados are open).
Just keep in mind, they are not "bass heads". The bass is more realistic, not over accentuated or punchy. Very low response, but again, realistic.
I've had them for about 1.5 years, and use them 4-8 hours a day, 5 days a week. I still look for a better set for the same price, and have yet to find anything that compares.
I guess I've put about 2000+ hours through them, and still am in love every time I put them on.