American Popular Song
Message board and directories of singers, songwriters, movies, and shows.
http://www.americanpopularsong.com/

Craig's BigBands and BigNames
Historic reviews and photos from performers of the 1940s, 50s, and 60s. Includes old time radio broadcast, quiz, and message board.
http://www.bigbandsandbignames.com/

Ian Whitcomb's Literary Corner
Includes articles on Rudy Vallee, Duke Ellington, Irving Berlin, and the first crooners.
http://www.picklehead.com/ian/literary.htm

JD Hay's Crooners
Library of songs in WAV format, including those by several pop artists and a 1950s collection.
http://www.angelfire.com/retro2/croonerjd/index.html

Parlor Songs
Collection of popular and classical sheet music from the 1800's to the 1940's, cover art, audio samples, composer biographies, and articles on the history, styles, and themes.
http://parlorsongs.com/index.asp

Jukebox: American Popular Music in the 1930s
Includes 40 audio files, with background and commentary.
http://xroads.virginia.edu/~UG03/Jukebox/front.html

Wikipedia: Melodic Music
Defines "melodic" genre as the vocal-oriented popular American music style that came after big band music but before rock and roll, as exemplified by singers like Perry Como and Margaret Whiting.
http://en.wikipedia.org/wiki/Musical_genre#Melodic_music

Topix: Vocal
News about vocal, collected from various sources on the web.
http://www.topix.com/rss/music/vocal.xml