Never really liked the pop music played on the show. Most of it, including the opening theme, was by artists who arent even around any more. That has the effect of dating certain episodes to me when the rest of the show has a timeless feel to it when it's just accompanied by an instrumental score. .
Supernatural uses another approach which I really like and that's using classic rock n' roll in all of their episodes (Kansas, Zeppelin, CCR, etc.). You get a timeless feel to it, since those songs are classics and not stuff from one hit wonders like SR-71, All American Rejects, James Carrington, etc.