Quality Headphones at Decent Value

Sennheiser 555 or 595

Audio Technica ATH-m50s.  
It sounds so good and is so comfortable.  
I just got mine last Sunday.  

And the Price is good too. ~$110  

Grado Prestige SR80.

+1 on the Audio Technica ATH-M50 suggestion. My first higher quality headphone purchase were a pair of IEM's by Head Direct (The RE0's). They received rave reviews, and do sound quite good for their size and price ($80). When I bought my ATH-M50's though, the sound is so nice - easily my preference when listening over headphones. I've had mine for several months - they are very comfortable to wear, have great bass which doesn't overpower, the entire overall sound is detailed and pleasant. I paid $120 for mine and couldn't be happier. They're good at isolating external sounds as well. You'd be hard pressed to find better headphones without spending more than $250.

I've used mine for gaming briefly, they are excellent in that purpose as well. I heard many sounds in L4D that I did not hear over my speakers (And I have relatively nice Logitech Z-5500's hooked up). I listen to Hardstyle which is extremely bass heavy and they sound fantastic playing it, I also listen to jazz, 70's rock, electronica and can honestly say they are very diverse headphones - they play every kind of music I listen to excellently. I have a rather extensive home audio setup, but I must say I really like just putting the ATH-M50's on and letting the tunes flow - listening to the details you may never have heard over speakers. These are the best all around package you're going to get, some of the others you mentioned excel with certain music but don't do so well with others. I'd suggest the M50's for their diversity given you listen to a varying range of music and applications. I do not think you will be disappointed, as I'm rather picky and loved these headphones (I did purchase them based on other reviews as I had no where local to sample them beforehand).