What are some examples of music for guitars with non-standard number of strings?

I recently read an interesting book on guitars (basically a coffee-table book I found at the library, but it had lots of photos and information on the development of different guitars over the years), I never really paid that close attention to the variety of guitars available even among acoustic instruments. What was really fascinating was the number of guitars that had odd numbers of strings--5, 7, etc. (along with those guitars with multiple necks). I know I've seen sheet music for songs originally accompanied by 7 string guitars. I've also personally owned a 12-string guitar I found at a pawn shop (covered in dust and nicotine residue). I didn't like it and eventually got rid of it because it probably needed some sort of set-up and I didn't know about those things back then. But what about those other unusual guitars with added bass or treble strings, and such? Any example of music-written music or recordings that you know about? Electric or acoustic--doesn't matter. Just curious.