Songs that have stood the test of time.

If the test here is that the song invites reinterpretation, I'll nominate two from Todd Rundgren.  I love both songs and both reward a great voice:

Pretending to Care
Love is the Answer


Both have been covered to great effect many times - but Love still awaits the definitive interpretation IMO.

Speaking further of Dave Mason, he's out touring right now (with Bekka Bramlett, daughter of Delaney and Bonnie Bramlett).  I love Mason's guitar playing and I've got tix for his local show here in the SF Valley on December third.