As a professional you hardly can live without it:
www.musicalchairs.info
www.klassika.info

Probably the most important & most helpful website for on art-song:
www.recmusic.org

Some wonderful singers:
www.martinaschilling.de
www.klemenssander.com
www.kulmann.info
www.evameier.info

Some information about Peter Feuchtwanger:
www.peter-feuchtwanger.de/english/startenglish.html

For everyone who loves good documentaries:
www.oval-film.com