JDS Labs Assembled Objective2 Headphone Amplifier - Reviews
Pros: Transportable, sound great with LCD2s, cheap
Cons: a little big for your pocket
This is a perfect transportable amp with size similar to Hifiman HM801.
When couple with a Sansa Clip, the sound quality beats my previous HM801 w/o external amp.
It drives all of my headphones very well, including LCD-2s, DT880s/600ohm and Westone ES3Xs (IEMs).
Overall sound quality is easily at the same level of full size amps costing around $300-500 USD. It does not seem to add any flavor to music, more like wire with gain. Very transparent.
Some of my previous impressions can be found here:

yes and no. a lot larger than some other portable amps.
HM801 is just bloody huge.
You know you're an audiophile when your portable amp is a hundred times the size of your source.
Pros: Drives my HE-500's, Acts as an amplifier should; as the backbone of the system
Cons: Not Exactly on the go Portability
[size=small]It's transparent, and neutral with a slightly warm tilt. Noise floor is non-existent and great for IEMs. Look elsewhere if you want more bias in an amp.[/size]
I just bought one of these in kit form, I got the case, engraved front panel, AC power adapter, and all the parts for $102. I do not intend to use it as a portable amp so I did not buy the batteries. The assembled unit comes with batteries but no AC power adapter, the adapter is $15 extra.
It took me about 2 hours to build the unit, you should be familiar with building kits if you go this route because there are no step by step instructions. You can download the schematic, parts list, and some construction guidelines you really have to familiar with electronics to build this yourself.
One it was assembled I ran through some checks to be sure the unit was working correctly before plugging my headphones into it. Once I was satisfied it was working correctly I hooked it up to my Imac and plugged in my Sennheiser HD600's. I have about 4,000 tracks on this computer and they vary from 256kb MP3's to 192kb 24 bit tracks. The sound is clean, balanced, and very smooth; if you have good source material you will be happy with this amp.
I'm sure there are better amplifiers but I don't think anything can match this little amp at 4X it's price.