Apart from the mountain of material in the members area at LearnCigarBoxGuitar.com, I've been gradually building a stack of free stuff too. Check it out.
Specifically for cigar box guitar players this course will get you started on understanding music theory so that it's actually helpful. It's referenced throughout the rest of the site and will be useful for anyone interested in making music, but particularly crucial when you get to the more advanced courses and workshops.
Just for 3 stringers, use the filters to find just about any chord you can think of.
With all the extra options that extra string gives you you need a bit more information than sa simple chord chart, although there's one of those too.
How to cope with playing chords when you've only got three strings.
17 Blues turnarounds for 3 string guitar, with accompanying video.
I've got a stack of videos on YouTube but they can be hard to find and rarely presented in context. Not any more.
A short Workshop for new players explaining the basics of the guitar and how to play it. A must have for brand new players.
There are a bunch of backing trax in the members area. Here are a few samples, all in the key of G.
Mainly theory, this one is all about constructing grooves.