If I got a song from another page it should be credited on the song page. Most of the older songs are in multiple songbooks, and I (quite frankly) have given up getting them all cross referenced for now. I've scanned the old songbooks and put the scans up, as current songs are the primary focus and the scans preserve the history. This is a list of places that helped me track down sources (especially original tunes for filks.)
Google
Always a good starting place
Lesley Nelson's Folk Music Site
A great resource for tracking the history of folk songs. Folk and Traditional Music and Popular Songs, with Lyrics, MIDI, Tune Information and History behind the folksongs and ballads. Irish, British and American Folk Music including Francis J. Child Ballads and Sea Shanties.
Erich Hlodowechssun's Songbook
When I have a question about a folk song, or an older Calontri song, or (really) any song ever written, there's a good chance that Erich either has a good idea where to look, knows exactly who, why and when the song was written, or has researched the history and can give me chapter and verse! Really, if you have an interest in song history, and are at an event/post revel with Erich, I can't overrecommend talking to him.
The Digital Tradition Folksong Database
This is where all the folksong people hang out :-) Fantastic resource for lyrics, MIDI's, and general information. Not as much background information as Lesley Nelson's site and the MIDIs are just melody.
Kingdom of Calontir
My SCA Kingdom. Without Calontir and the people within it, there is no point to these pages.