I'll give another plug for the XDA-1. So far, I've compared it to a few others in the price range, like the V-Dac II, rDAC and DacMagic and have stuck with the Emotiva because it sounded the best in my system. With all of these lower price DACs, I really don't think that any one is head and shoulders above the rest.
What I've been wanting to try is the Schiit Bifrost. The specs look really good on paper and at $350 (I don't need USB) it's begging for a test drive. The only thing holding me back is that I've read a couple of reviews by users saying that it's just a different flavor of inexpensive DAC that isn't a significant improvement over other inexpensive DACs, if any improvement at all. Just more of the usual stuff being a "great bang for the buck" as are all of the other DACs that have already been mentioned.
Personally, I consider the XDA-1 to be a heck of a deal at $250, shipped. Really, I could have paid $400+ for it and would have felt that I got my money's worth. My little mid-fi system still surprises me sometimes when I get my hands on a really good recording.
As many have said, you really don't see a significant improvement in sound quality until you get into the $1K+ range of DACs.
As food for thought, I will mention that the Peachtree DAC It is on computeraudiophile's list of recommended DACs and they comment that it's the lowest priced DAC that has ever made the list.