Of the headphones I've personally heard, I'd recommend the Audio-Technica A900 or Denon D2000. The main reason is that they offer a bridge between typical audiophile and mass appeal sound that most people want initially. The latter is typically more bass impact oriented, and both offer pretty good bass, but also are decent at other aspects.
I know some don't find the A900 to sound all that good, and I'd admit its getting long in the tooth but, to me, its a great all around headphone. I'd actually say the Denon is mostly similar but a bit better, its slightly more comfy, and has better bass. Both can be pretty easily modded a bit (and you can buy better earpads for both as well). The only issue is price, where I'd say $150-180 for the A900s and $170-200 for the D2000s, but I don't know that you'd be able to get them new for that price. There's someone selling A900s in the For Sale forum for $150, and you could buy some replacement earpads from AudioCubes.
I've read some people say the M50 is better than the A900, but I haven't heard it myself so I can't give offer an opinion, I do know its a pretty well regarded and often recommended headphone though.
Two other headphones that fall close the D2000 and A900 are the Ultrasone HFI-780 and the Beyerdynamic DT-770. I've only heard the HFI-700, and Ultrasone tends to be polarizing for most people so I don't know that I'd recommend it, but the sound and price is fairly similar (but also has its own uniqueness) to the others though, and it's more portable. The DT-770, I have only heard the Pro version of, and it, to me was too strong in bass, but I've read that the normal version is more balanced.
There's also the Ultrasone Pro900 but you would have to get used to get it in your price and again, Ultrasone isn't for everyone. The W1000 is similar (probably only in your range if used), and I wouldn't recommend it because it has a pretty unique sound that I'm not sure most people would like (I didn't).
Another option, and since you'll be going to classes might be a bonus is looking into high end IEM, or maybe if nab someone's customs from the For Sale forum and get them remolded for you.
That or you could maybe go for a portable like the ESW9.
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If your budget is $300, make sure you have enough left over after you buy headphones to get an amp (if they need one) or you'll be dissapointed. You could (just an example) do something like this: Ath-m50 ($115) + Nuforce Udac ($99) / another amp if you want ($100+). The udac will give you better sound than computer headphone out and it also has an amp (weaker than some, but I've heard of good results with m50 + udac).
That's not a bad recommendation.