More to choose from here than I would have imagined...would love to see the results of a "shoot out" with high resolution headphones.
So a search over at HeadFi.org. There are numerous shootout threads pitting one or two of these against the other. Like here, take everything with a grain of salt...in fact, take it with more salt IMO - it is a different crowd over there, with plenty of crossover. There's a member there, Skylab, who's been doing an ongoing shootout that focuses more on the small headphone amnps, rather than the DAC's.
In general the Pico DAC and the iBasso D4 DAC are two of the most respected in the smaller offerings. I don't use a laptop interface - I simply use an LOD cable out of my iPod (older model or iPhone), into the D4 which is straped together with the iPod. The kit fits neatly with some accessories into a Lowepro Rezo 50 digitial camera bag. You didn't ask about portable headphones, and that's a whole other ball of wax.