My favourite Shatner performance is another live one, but it doesn't seem to exist on YouTube. I downloaded it ages ago from elsewhere. I think it's a clip from the Tonight Show, or some other US night time chat show, and he's performing Pulp's "Common People" with Joe Jackson.At the risk of scaring off people...
That and the AFI thing where he's singing to George Lucas...
Also, as my girlfriend once pointed out, his Mr Tambourine Man sounds as if he's being fellated whilst singing.