The washboard is just the beginning. Let your imagination go wild in adding cowbells, pots & pans, cans, wood blocks, etc. to add variety to your rig.

"Scratchy" Ron Goad plays washboard in my band. The All New Genetically Altered Jug Band.

You can hear some fine rubbing here:

http://www.myspace.com/ANGAJB
and here:
http://www.geocities.com/ANGAJB

Historically look for recording from Washboard Sam, the Washboard Rhythm Kings, The Washboard Wonders, and many of the old jug bands.

Gutbucketeer