[marone]

Give the SuperLux line a listen. I am liking the 668b's. A very good set of cans for under $30.

 

[ev13wt]

Bump your bedget up to 200/250 bucks. Or get a 50 dollar Sennheiser PX-50. The gap from 40 to 100 ain't that much different sound quality wise. Not really. 200 and up towards 500 is the next big jump.

Its my take on it, if you are gonna do it, do it right. If you want to spend only 100 bucks, don't ever listen to better headphones because... You will want them and will kick yourself for not getting into better sound right away.

 

[Tundra tunes]

The Sound Professionals website lists new M50's in sealed factory box for $99.  If you are on Ebay you can find Phillips Uptowns for $80, or Skullcandy Roc Nation Aviator's for $99.  
 

 

[urbanshocks]

I'd go with Grado out of the ones you listed. Either model would do.

 

[Shaffer]

I'd go with Grado out of the ones you listed. Either model would do.

As would I.

 

[ShermyWormy]

I have the SOL Republic Tracks Ultra and they sound awesome and they costed about 100$ on sale!

 

[Star2806]

Philips shl3300, they have a balanced signature similar to the Philips x1, but with more sub bass and slightly less upper treble.  Soundstage is excellent for closed back headphones and they are very cheap, an absolute bargain at £25 in the uk. 

 

[doni124]

I have the Sol Republic Tracks and I only bought them for about 40 bucks new and I have to say they're not bad. They have enough base and while they have more base then treble it seems to balance out a little.

 

[sikki-six]

Creative Aurvana Live! is one stellar product in this price range. Very good overall sound, with nice presence of sub-bass and treble chime too. I find the SQ to be above Senn Momentum and V-Moda M100, which cost many times more (and I own all three). The only downsides: kind of cheap build and very low isolation for a closed headphone. 
 
I've had Grado SR80's too, and they lose in pretty much every category. They have weak bass and an overly forward signature in the higher regions. They don't sound very open, even with the open design. But, I must admit, the slight V-shape in CAL!'s frequency range is a good thing for me (I'd bet most people would agree, especially for longer listening sessions). Comfort is only adequate because of the rough pads. 
 
EDIT: Audio Technica M50's have a very strong V-shape in the sound sig. Treble can be harsh and metallic, bass is often boomy and all over the place. These have a kind of shouty sound, with very little air. I find them exhausting for longer sessions. This one is way over-hyped, for some reason. At least they isolate quite well.

 

[cpt000]

Yamaha HPH200 has come down significantly in price and you can find them for around $90 - very detailed, neutral open headphone.

 

[ptolemy2k6]

I would also specify whether you want open or closed? You could also go for sony mdr-v6 and they can be had for $60