uDAC3

“The NuForce uDAC3 is high quality and because of its small size and weight it can easily be used on the move. It is primarily designed for use with a notebook and it clearly improves the sound quality of a notebook. Furthermore, it completely eliminates any annoying background noise.” 
 
Positives:
+ High quality processed
+ Small size and low weight
+ Supports windows and OS X
+ No installation required
+ It clearly improves sound quality