HighResAudio
http://www.highresaudio.com/

2L- the Nordic Sound
http://www.2l.no/

AIX Records
http://aixrecords.com/

Blue Coast Records
http://bluecoastrecords.com/

Bowers and Wilkins - Society of Sound
http://www.bowers-wilkins.com/Society_of_Sound/Society_of_Sound/Music

Cantaloupe Music
http://www.cantaloupemusic.com/

Chesky Records
http://chesky.com/

Gimell Records (96k/24bit, 48k/24bit, 44.1k/16bit of the The Tallis Scholars)
http://www.gimell.com/

HDTracks
https://www.hdtracks.com/

High Res Music
http://hiresmusic.com/homepage.html

High Definition Tape Transfers
http://highdeftapetransfers.com/storefront.php

High-res download test bench (free samples only)
http://www.2l.no/hires/

Hyperion Records
http://www.hyperion-records.co.uk/

Internet Archive (dot org) - has some high res available - including Hungry Lucy!
http://www.archive.org/details/audio

iTrax
http://www.itrax.com/

LessLoss Audio - Free Sample High Resolution Audiophile Recordings
http://www.lessloss.com/high-resolution-audiophile-recordings-c-68.html

Linn Records
http://www.linnrecords.com/index.aspx

Qobuz
http://www.qobuz.com/

Reference Recordings
http://referencerecordings.com/

Rhino
http://www.rhino.com/

See also the thread "Where to Download Lossless Music" and article List of Lossless music download sites.