Sorry, I can't just pick one song.
Here's a few:
Fenians, by Seanchai (sort of Celtic rap)
One Hundred Years, by Five For Fighting
I'll Love You Forever, by Priscilla Herdman
Come Away Melinda, by Uriah Heep
The Trees, by Rush
???, by Joe Satriani (excellent electric guitarist)
Out On The Parkway, by Michael Hedges (beautiful acoustic guitar or harp/guitar - "the guitarist from another planet", according to Will Ackerman)
Fxxx the Pain Away, by Peaches
Bury My Lovely, by October Project
Be My Number Two, by Joe Jackson
6 In The Morning, by Ice-T
...And Left Banke, and Spirit, and Creed, and The Association, and Peter Paul & Mary, and AC/DC, and Steeleye Span, and Moby, and Jim Croce, and Harry Chapin, and Brother, and Devo, and Caravan, and Boston, and Kansas, and Chris Rea, and Vusi Mahlasela (?sp?), and Enigma, and Apotheosis, and Rick James, and Alan Stivell, and Enter the Haggis, and........
Too hard to decide!