Well, I'd like to add http://www.highresaudio.com/ as high quality download site (if that has not been done yet).
They offer only high-resolution 24-bit albums at sample rates from 88.2kHz up to 384kHz. (perfect for my new 24/192 DAC :-))
As far as I can tell (I downloaded only one classic album a few weeks ago)they seem to keep their promise of being "a perfect companion for audiophiles". Not cheap though.
Has anyone else tried their FLAC, AIFF and WAV downloads?