I like some of these, while others...
Across the Universe was, I thought, fantastic. Bought the soundtrack, too.
I looked on Youtube but couldn't find some of the covers I've seen performed.
YES did Obla-di,Obla-da as an encore on tour once that had the audience bouncing, and I saw Pat Benatar do Paperback Writer (the less said, the better) but the one that sticks out is Billy Joel. He was at ASU Activity Center on the Uptown Girl tour and right in the middle of Piano Man he segued into Norwegian Wood. It was amazing. Just amazing.
One other-I saw Clapton perform and he introduced a song by saying he'd been on the phone with a friend before the show. Since the guy was on his mind, he was going to do one of his songs. He performed Strawberry Fields. It was a very sweet, soulful cover, as you can probably imagine.