Every once in a while you get that rare gem: a rock and roll tune with just words but little or no musical accompaniment. I meticulously combed my MP3 file collection (which is very large) for a capella tunes but could find only five, and all of them from European groups. Groups in the former Eastern Bloc seem to be especially good at a capella tunes due to the history of pop quartets and choirs in their countries.
Here are a few good tunes:
Mocedades - Jimmy Brown, Part 1 (Spain)
ER Meeskvartett - Vaike Sunfoniett (Estonia)
Trio Relikt - Pozhar (Russia)
4TET - Ja to tady vedu (Czechoslovakia)
Gaya - Sosna (Azerbaijan)