[bukujutsu]

The SR850s too, since they're rebranded, but with only one cord, no removeable cord, and the impedance is 32 ohm instead of 56. 
 
The SR850s are 34$ on eBay, the HD668Bs are $50. 
 
There are so many headphones out there and as the time goes by things can go unnoticed. 
 
Some people think the Maxwell DHP-II is better, but there may be problems with build quality. 
 
 http://www.head-fi.org/t/501637/maxell-dhp-ii-review-impressions-giant-killers-answer-contenders/15
 
I think headphones can be horribly overpriced to the the influence of psychological biases, such as the placebo effect, and the difficulty in quantifying quality. I enjoy economics, so to me this seems like a guaranteed opportunity for inflated prices. Due to that, I'm keeping my price range below $60. 

 

[Emospence]

Add Superlux HD681 to that list, along with Panasonic HTF-600, both come close in terms of quality and value IMO
 
But to answer your question, better than 668B at their asking price.. Tall task.

 

[boomhaur]

I am enjoying my superlux 668b, when I was looking at headphones this was the best bang for the buck I could find when focusing on sound quality.

 

[Kerry56]

The Koss DJ100's are a contender in this price range.
 
And I bought my Creative Aurvana Live! set for $55 a few months ago, but good luck catching them on sale now. 

 

[valerianaoff]

Superlux HD661

 

[Supertoaster]

The Superlux HD681 are much cheaper then the 668b.
 
Think of them as a slightly thinner sounding, more aggressive, bassier, flatter, slightly funner sounding 668b. Some people claim the 681 is more enjoyable but it's more of personal preference. 

 

[Emospence]

Quote:

The Superlux HD681 are much cheaper then the 668b.
 
Think of them as a slightly thinner sounding, more aggressive, bassier, flatter, slightly funner sounding 668b. Some people claim the 681 is more enjoyable but it's more of personal preference. 

How do you get "much" cheaper than something already so cheap 

 

[Supertoaster]

Quote:

How do you get "much" cheaper than something already so cheap 

Superlux magic.
 
The 668b's do have slightly more detail and better soundstage too. 

 

[joshuadapitan]

HD661 for the imaging and overall balanced spectrum and smooth response with a sweet sub-bass rumble, the treble is Grado level though.

 

[GuywhoLikesHIFI]

Check out the Takstar Pro 82 and the Bosshifi B8.

 

[god-bluff]

Beyerdynamic DTX910?