Best in terms of pure value may be the mhdt Constantine DAC used for $350 or so.
Its SS rather than tube so it seems to fly under most peoples radar but is a giant killer IMHO. My digital with this compares quite favorably even to some of the best vinyl systems I have heard.
Roku Soundbridge for $129 new at Best Buy a couple years back may be the best investment in sound overall I have made, especially combined with the mhdt DAC.
Also, Ipicked up a pair of OHM Super Walsh 2s (100S3 drivers) for $600 used here on agon a few years back and that has been another giant killing cornerstone.
DNM reson ICs for under $50 also a fantastic score!
I know somebody who picked up a pair of OHm Fs for free that turned out to be in good working order. Can't beat that!!!