4Praise.com hosts thousands of free Christian mp3 songs of varying quality. All of the songs are submitted with full permission of the copyright holders and is 100% legal.
You can search through the website either by looking through the song list or artist lists. A usefull addition is the ability to see the most popular songs and artists – this is particularly important as the musicians included are not mainstream.
A big improvement would be to have the songs also filtered by genre. With over 4,000 songs there is a lot to trawl through with little to guide you on the style of music.