Emil's Phish Tabs has a posting of "Ginseng Sullivan" which I think is a fun one.
http://www.emilstabs.org/wiki/index.php ... g_Sullivan
It's Phish's version, I don't know how close it is to the original having never heard it. Also Guitar tab universe has a posting of "Constitution Man." A song I'm not too familiar with.
I know that he does "You Are My Sunshine" on the O Brother soundtrack. (Which I think is an EXCELLENT disc.) And the tablature for that is available for purchase through the following link:
http://www.readthemusic.com/musicians/O ... t_Thou.htm
You also might want to check Chordie