Since there's already so much conflicting information in this thread, I figure I may as well throw in my two cents.
Audio-Technica ATH-M50 ($120) - Great all around headphones, they're pretty good in every aspect, but also don't excel in any. Probably the most "yeah, alright" headphones you'll ever see, there's really not much to say about them, but there aren't any complaints either. Very nice for someone who isn't looking for a particular sound and wants some nicely built headphones. They're also very comfortable.
Sony MDR-V6 ($70) - These headphones are a studio standard, and very cheap to boot. They have a very neutral sound, which is useful for mixing, but some people may find that it sounds "flat". They're also quite comfortable, but you'll have to replace the ear pads eventually, as they're not the highest of quality.
AKG K 240 MK II ($140) - These headphones have a semi-open design that allows it to have a much greater soundstage than the other two, giving everything a much more open sound. One problem with the semi-open design is that it leaks a lot of sound out, so if you want to listen to music loudly without letting people hear it, these probably aren't for you. They're also the most comfortable cans you will ever put on your head, seriously.
Grado Prestige Series SR-60i ($80) - Another open designed set of cans, making for a nice and detailed sound. These headphones are also very small compared to the others here, and are great for packing away and bringing along when travelling without sacrificing quality like you do with most small headphones. Some people don't find them comfortable, so if you're not a fan of the on-ear design these might not be the best choice for you, comfort is a huge factor when buying headphones. Even if they sound great, you're not going to want to use them if you find wearing them annoying.
Sennheiser HD 558 ($180) - These headphones have a a very neutral sound, and it's also quite detailed. Once again, these cans have a great all-around sound. Nothing too flashy in one end or the other, but competent enough in each side to please anyone. They also have a bit of a sound leakage issue, but I wouldn't consider that a big dealbreaker. The real problem is the build quality. Sennheiser is infamous for cracking plastics and snapping headbands. It shouldn't be too much of an issue, but if you do buy these you best be careful with them, and grab a warranty on them if you can.