That would be a whole discussion in itself :-)
I am partial to the Leckerton products personally. No special drivers required and they just work, and sound great.
http://www.leckertonaudio.com
I have the UHA-6S (I have a review posted here and there are others), the UHA-6 drops the optical input for a few dollars savings and they also have the less expensive and smaller UHA-4.
Note that these are DAC/Amps which is what you would typically want for a portable application.
I am currently using a (long out of production) iRiver to give me mobile digital audio output.
Reducing my device count by one (I use a Nook Color for reading but could replace this with a generic tablet), and not having to rely on an ancient piece of equipment is extremely attractive to me.
Quote:
Originally Posted by
4DThinker 
I've got the Asus Transformer with 3.1 on it, but not the dock (yet). There is no USB port on the tablet itself.
I've also have the Acer Iconia tablet, and it is supposed to get 3.1 sometime this month. It has one regular USB port on the side. I'd be happy to test for DAC compatibility, but I'll need someone to point me to a reasonable DAC to get.
Edited by sbradley02 - 6/2/11 at 10:16am