Some resources I have used include:
Ken Perlman's "Fingerstyle Guitar" - a really good instructional book which goes from very simple fingerpicking to pretty complex ragtime arrangements.
Happy Traum's book of fingerstyle guitar arrangements -- I can't remember the title at the moment, but it's a re-issuing of two books that he put out way long time ago. It has arrangements of lots of Mississippi John Hurt, Mance Lipscomb, Rev. Gary Davis, etc.
One book that was very helpful when I was just starting to teach absolute beginners was "Country and Blues Guitar for the Musically Hopeless" by Carol McComb (at least I think that was the title -- my brain is on vacation today!). It was a very funny, accessible, how-to-play guitar from the very beginning that was put out by Klutz press. It came with a couple of cassettes. What I liked was how she boiled things down to very simple principles, gave people some great songs to practice, and made it very fun.
There's an old beginning guitar book by Earl Robinson that also gave me some great ideas. I think I picked it up used at a yard sale or someone gave it to me.
I also have various songbooks like "Rise Up Singing," "The Folksinger's Word Book" and books of artists like Hank Williams, The Beatles, etc. They come in handy!
And I also do consult the internet. When a student comes in asking about learning a particular song, I can quickly find words and sometimes chords, which I can cut and paste to make a songsheet with chords. And if I don't know the song, we can often find something on YouTube or other sites that have streaming music, so that I can help them create an arrangement. Sometimes I will buy a song from iTunes paarticularly because a student asked to learn it and I want to be able to consult the original closely.
Recently I discovered Bob Dylan's website has all his lyrics with links to recordings that you can listen to. Very handy, since his songs come up a lot in lessons.