For me, the Levon Helm concert this past Wednesday takes the cake…and the fork, the plate, the table it’s setting on and, well, I think you get the idea. Guest appearances included:
Little Sammy Davis
Robert Plant
Sam Bush
Buddy Miller
John Hiatt
Alison Krauss
Sheryl Crowe
Steve Earle
Billy Bob Thorton
Delbert McClinton
Allison Moorer
Billy Bob introduced the band and then, later on, came out and sang a song. Who knew he could sing? He wasn’t great, but not nearly as bad as I expected.
This show was INCREDIBLE. Though I’m not really a fan of Sheryl Crowe or Alison Krauss (never even heard of Allison Moorer), I love all the others…and, of course, Levon was great 
And, incase anyone is unsure of who Levon is, he’s the singer/drummer: http://www.youtube.com/watch?v=38JpAMG65Dg
It was also recorded for TV and DVD. shew…I’ve still got a high from it.
At some really lame concert an old boyfriend drug me to was the best guest appearance ever, Iggy Pop. That guy is legendary!