I like a lot of the artists that have been mentioned, but different songs.

Joni Mitchell - my favorite song of hers is Urge For Going. Her recording is superb, so is the one by Tom Rush.

Bob Dylan - Visions of Johanna.

Phil Ochs - What's That I Hear (or his setting of The Highwayman).

Judy Collins - Anathea.

I'll second the nomination of Get Together, but I prefer the Mitchell Trio to the Youngbloods.

Tom Lehrer might seem a little out of place here, but I'll still nominate Vatican Rag.