Steeleye Span, the English electric folk-rock band, once did an a-capella version of Rave On, by the rock and roll (and now it seems, folk) performer Buddy Holly. You can't get much more cross-fertilisation than that.

The English folk duo, Mr. Fox (Bob and Carolanne Pegg) did a song called "Aunt Lucy Broadwood" which seems to me to be the first (and so far only) example of a new genre called "Folk Rap". Aunt Lucy Broadwood as many of you will know was a folk song collector (I think contemporary with Cecil "C." Sharp, or D. Flatt as he is sometimes called, brother of L. Flatt who performs with E. Scruggs).

I sometimes sing in the Key of E. Scruggs