Here's a neat tune called "Bound to Have a Little Fun" in the key of G. I like the little surprise twists. The "A" part is 8 measures repeated but the "B" part is 12 measures repeated. Neighborly Music has a tutorial of this tune complete with video clips played slowly. Click here to watch their rendition of the tune on fiddle, banjo & guitar.
Here's a few folks having fun with the tune:
Try it on the harmonica!