Nilsson - Poli High (Live on The Skip Weshner Radio Show) 
Performed during an LA radio show where Harry Nilsson live demoed some of the tunes he was working on for his upcoming album/animated film The Point, this is definitely my favorite version of the song. For my taste, the official version got a little over-produced for the simplicity of the song itself, whereas, here, we get Harry solo at the piano, which is always going to be tough to beat.
One of Harry's great skills was his ability to harmonize, as his incredible adeptness at overdubbing on his albums makes crystal clear, but here, with no multi-tracking to play with, you can still feel his harmonic sense in the way that he truly sings with his piano rather than on top of it. It's a subtle thing, but the loveliest things often are.
As a bonus, there are some other great song performances here as well as prescient warning about simplistic demagogue TV politicians from the host, Skip Weshner, at 58:38.