Harpo plays the harp. I've heard the harp played a little bit in some pop music I believe, but can't remember where I heard it. It might be interesting to adapt it to experimental music.
I thought about Harpo Marx after seeing a 5 LP set of harp music from the 1600's to the 1900's in a thrift store. I went back and bought it for $1 per record ($5 total). When I get a chance, I'll fire up the tubes and listen to it.
For a beautiful and timeless electric harp recording, try to find a copy of Andreas Vollenweider's "Caverna Magica (...Under The Tree_In The Cave....)". Magic stuff.