www.recmusic.org
A great site for all of those who like to know what the Lied they sing is about and who want their public to know that as well (though a proper pronounciation and imagination should do it too)

www.aria-database.com
The same information for big voices and great actors

http://imslp.org/wiki
The free public domain sheet music library


www.bach-cantatas.com
Everything about Bach's Cantatas, including scores of all of them.

www.vvhl.nl
The site of a dutch society that organizes numberless song recitals in private houses all over the Netherlands.

www.israelgolani.com
An amazing lutist

www.sabinewuthrich.com
A very good Soprano

www.dlib.indiana.edu/variations/scores/scores.html
Opera scores online