Oops! I just went to the NBC/West Wing website and learned (from their FAQs) that the season finale this last spring was the "posse comitatus" episode. (I had thought the "posse comitatus" episode was the one in which Bartlett ordered the assassination of an official from another country.)

So the song is definitely Cohen's "Hallelujah," but it was sung on the show by Jeff Buckley.

Look for "Hallelujah" in the Forum and you'll find the lyrics and chords.

Genie