Glenn Kaiser, Darrel Mansfield and blind Willie Johnson are the one's i know of....
these artists were recommended by my missionary friend about a few years ago and have been a big source of inspiration to me ever since..
hope this helps..
Godbless.
EDIT: check this site www.grrrrecords.com
Since the term "Chrisitan" connotes a unique meaning it does today (Christian as in "born again"... tama ba?), I'm not sure if Blind Willie Johnson was actually a Christian. But he certainly was religious and played traditional black spirituals/gospel. He's the best at it, IMO. But there a lot of other great 'guitar evangelists': Mississippi Fred McDowell, Blind Joe Taggart, Blind Joe Reynolds, Reverend Gary Davis, Sister O.M. Terrell, Two Gospel Keys, Blind Mamie Forehand, Reverend Edward Clayborn, etc.
I love this stuff.