Personally I use a pair of Sennhieser HD280 Pro headphones for arranging my stuff, then I do my mixing on a pair of M-Audio BX-5 Studio Monitors with a Yamaha subwoofer. The cans are good, and so are the BX5s. The sub leaves a bit to be desired in the frequency range department. Anything above like 130-150 hz isn't so great. All in all it's not a bad setup by any means. Everything is fed by my Yamaha MG12XU via USB 2.0 from my Alienware Area51 R2. Expensive, yes, but it does the job. Is also why I'm broke ;D
Just my 2 cents.