Kazza, that's a GREAT song, and would be really fun (and appropriate) for a first dance. (It's Chuck Berry's "You Never Can Tell".)
My sisters and I went for uptempo songs. I had the honeydripper, "Follow You Follow Me," by Genesis (well, it was the '80s). My sisters got married in the '90s; one used "I only want to be with you" by Hootie & the Blowfish, and the other, with her great sense of humor, used R.E.M.'s "It's the end of the world as we know it" - everybody young enough to know the song was hysterical.
Horselady, your son and his fiancee are to be commended for wanting to choose something fun. How about asking friends/family to email them suggestions? They would probably end up choosing something entirely different, but it would be fun to read their ideas.