If you're looking for something closed or sealed, I HIGHLY recommend the AKG 271. It's totally sealed, and it sounds phenomenal, unlike most sealed cans I've heard. It has a great bass response, and that standard clarity that accompanies AKG headphones. The cable is detachable via mini-XLR, which makes it a cinch to swap out different cable upgrades (I like to use a DIY Cardas cable with it). It's really comfortable, also. It has the AKG suspension system, which just automatically adjusts to your head, and stays that way.
It most definitely needs a headphone amp to reach it's full potential, but a decent amp can be had for $100 or under (HeadRoom's "Total AirHead" amp is what I like to use when I'm out and about with the K271. It's small and sturdy like the headphones, sounds great and has a 40-something hour battery life on three AAAs)
If you're not after a sealed can, then all of the above recommendations are certainly worthwhile. I love Grado headphones. They're the warmest and most musical I've ever heard. SR-60s are great without an amp, SR-80s are better than the SR-60s, IMHO, but only when used with an amp, because the low end opens way up when amped. The unsealed, open AKG 'phones I've heard have only really blown me away with the 601 and 701. They're pricey, but certainly worth it. Like the 271, I find them to be very "clear" sounding and uncolored.
Sennheiser HD650 takes the cake, I think. It's just ASTOUNDINGLY accurate, and images like crazy. I don't own 'em, but I loaned a pair from a friend for a few months, and had the chance to really absorb them. They seem to earn their keep for the pricetag, which is considerable.
The HD595 is great also, and considerably less expensive. I find it to be a great "movie" headphone, which sounds especially good when used while watching movies.
Well, there's my take on it.