(I know this wouldn't normally be considered an audiophile component but I thought I would list it here just in case there is interest. The converters are actually quite good and there is a lot you can do with this unit even if you aren't a musician or recording engineer)
M-Audio Profire 2626.
This is a great AD/DA that has seen use only in my studio. I'm the original owner and it never left the rack in my studio until I upgraded to another unit recently. It comes with the original cables and manual.
I have used this with both a PC running Sonar and a MAC running Reaper with no problems. From what I have read, for use with a PC, it does require a good quality Firewire card.
There are lots of reviews and information about this unit online and some helpful forums.
Link to manufacturer info;
http://www.m-audio.com/products/en_us/ProFire2626.htmlLink to reviews at Gearslutz;
http://www.m-audio.com/products/en_us/ProFire2626.htmlAsking $250 shipped in CONUS