It really comes down to budget as the range here varies significantly. You might want to check out the Benchmark DAC-1... the name almost says it all, its really the measure of DACs in the space. With the move towards digital sources, and specifically the computer as a source, the quality of the DAC in your chain is going to make a huge difference.
Also I just got a chance to listen to the Emperical Audio Spoiler at a recent meet... $6k but...wow, amazing quality. Its a tube DAC beleive it or not. I guess its hard to put into words, how it sounds, but it was impressive. If you have the money to spend, its worth it. Steve Nugent knows his stuff.
My current setup: WAV/FLAC -> Meier Audio Corda Opera -> AKG K701
