[warsharks]

noise cancelling is one thing but im assuming youre looking for something to cut you off while you work, which also means long periods wearing them.

in my opinion the best option is actually isolation and to that end a pair of earbuds with a set of custom fit tips could be a good option, i have some myself on a pair of etymotic er4 and theyre spectacular, complete isolation from outside sound and comfortable enough to wear for 8 straight hours

[Spoom]

If you're going the IEM route, try out some tips from Comply (http://www.complyfoam.com/), I find they get really good isolation.

As far as the actual headphones, I currently have UE 900s IEMs which are serving me well but I would probably compare other brands nowadays were I to buy again.

[bradknowles]

I tried the Comply tips. I hated, loathed, and despised them.

I found the triple-flange silicone tips worked much better for me.

YMMV, etc.....