I'm amazed that nobody has yet mentioned the Museatex DACs (Bidat, idat44, Bitstream). They rarely show up for sale, and when they do, they go very quickly. Bidat's used to appear for < $1K, but recently one sold for $3K in just one day. Then again, audiogon is not exactly a "rational" market :)
Nevertheless, if you ever see a Museatex DAC for sale, especially a Bidat, snap it up and get it updated by John Wright if it hasn't been upgraded already. It may well be the last DAC you'll ever own.