Hmmm. I wonder if your friend would like the five-volume Country & Western Gospel Hymnal - there's also a "best of" book if 5 books is too many.
There's a folkie gospel book called Gospel Singer's Wordbook, but it's hard to find.
Holler if you need something more specific.
For that matter, I really rely on a book called Heavenly Highway Hymns, which has a good selection of the old-time hymns.
-Joe-