Do you and your roommate share a room? If so, don't buy open headphones. They leak far too much noise at any significant volume and could end up disturbing your roommate too much. If you need a closed 'phone, wmax's recommendation of the Sony MDR-V6 is a good one (I'm using them now!), however, I really dislike them unequalized - they're overly bright in the 5kHz region. If you have an equalizer (software or hardware), they're a wonderful choice. I've heard good things about the Beyerdynamic DT770 (if you're a basshead) and DT250, but haven't heard them myself. I have listened to both the Sennheiser HD280 and the AKG K271. The Sennheiser is a good substitute for the Sony if there is no equalizer available, but the K271s are easily my favorite. They're simply a very nice headphone. They do many things well, my only complaint was thin bass (but still accurate and punchy).
I also own the Beyerdynamic DT880 and love them, but they're open.
Edit: I forgot to mention, I owned the HD580s for a time. They're certainly a very nice headphone and a good value at that price, but I found there to be too much emphasis in the lower mids and bass region. I didn't mess with it too long since I had other headphones I preferred at the time (AKG K501 and AKG K271). I've now settled to the Beyerdynamic DT880 (best headphone I've tried), the Sony MDR-V6 (best value WHEN EQ'd and needed a closed phone), and the Etymotic ER-4P for portables