NetHymnal.com
This is a wonderful site with "over 7,100 Christian hymns & Gospel songs from many denominations. You’ll find lyrics, scores, MI-DI files, pictures, history, & more." It also includes the history of hymns along with photos of the authors and composers, whenever available.

The SDA Digital Hymnal
Sing familiar hymns along with a choice of styles of musical accompaniment such as piano, organ, piano/organ, band, orchestra, etc.

Songs of Praise
"There are currently 417 songs in the database in 17 languages."