I can't see that anyone has mentioned musica viva in a thread here. This site's got sheet music you can download and perform for free with the site owner's blessing. Read his FAQ. This is all public domain, folk, classical and early music. As Frank Nordberg is a music teacher in Norway, there's a lot of norwegian folk melodies and especially hymns in choral arrangements. A golden opportunity for your choir to add something really original to its repertoire. He's scrupulous about not infringing copyrights but figured "it's time that those music publishers charging big money for old music that hardly costs them anything to print got some competition!"