Which DAC for computer based system?

I have recently gone to a digital music server using a G4 laptop, a 500 GB hard drive and a Waveterminal U24. I have ripped all of my cd's to the hard drive and I just figured out that I can get lots of great radio through my computer as well. I can now sell my changer and tuner if I want. I am thinking about putting my money towards a really good DAC since my computer is turning out to be the heart of my system. I can't believe I didn't do this sooner! I am rediscovering my music collection and listening to stuff I haven't listened to for years. It would not surpise me if we begin to see a lot of USB DAC's on the market very soon. What DAC's would you recommend I audition or seek out (I can probably spend upwards of 2K)? Thank you