teknokid:KevinOK:
Please consider avoiding "Dr. Dre's" headphone's. Yes they look cool, but you said you care about SQ. That kind of money will get you much better headphones from just about any other reputable headphone brand. Including an excellent Grado. But Sennheiser and AKG at this price level will also be better. There's a shortage of reviews on the Monster Beats (bar CNET, avoid) but their marketing blurp on their website tells me enough. There's a thread on them in the website I was hinting at earlier. Something with "head" and "hi-fi"...
Edit: If you are indeed planning to lug around headphones of this class it completely changes the game. Most headphones in this pricebracket have high impedance. They require more amplification than any MP3 player can accomodate. Look for a portable amp. Headroom makes good ones, even including a DAC (you'll need a player with digital out).
Ahh, I read the review on this site and thought they seemed quite good.
Where would you recommend I look for well priced headphones? I quite like the look of these, and Scan seem to have quite a good price on them:
http://www.scan.co.uk/Products/Sennheiser-Home-HiFi-Range-HD650-Headphones
Those are high impedance. You will have a very hard time driving those without an amp (it's impossible). You'll have to decide wheter you want to carry a portable amp around first. If not, go with low impedance models. I strongly suggest you take a look at the website I hinted at earlier which is the best source of info for portable gear I know.
Oh and the quick and easy answer, for your budget, is the Grado SR80. Edit: actually those are considerably cheaper than your budget, but I don't think it's worth getting anything better if you're not going to get an amp. Headroom lists a nice assortment of good headphones. I'd start there for ideas.