The Peachtree Decco that Knownothing suggested in a great piece of gear for the money. I'm using one with a Macbook Pro, streaming to an Airport Express and then through Toslink into the Decco. I can also connect the Macbook Pro durectly to the USB input of the Decco DAC.
It has a tube preamp section and I'm using the preamp outputs of the Decco to drive a tube amp, though the internal amp of the Decco is pretty good, too.