Saw Bryan Adams and Junoon once, it was amazing! the worst was Atif Aslam.

The best live bands I've seen are Death Cab For Cutie(x2), Stars, Amos Lee, Elvis Costello, Something Corporate, Motion City Soundtrack, and Thursday.
Worst live band was probably Ted Leo and The Pharmacists, Starting Line.
I also saw Bob Dylan in 2008. He was so drunk he could barely play. I hate hate hate!! to say it but he bombed. I adore the guy,but it was awful.

Memphis May Fire puts on a killer show!!!

I'll second COF as worst live band in history.

Best live show was Elton John. I haven't been to many though.

Karnivool are by far the best band I've seen live. I am yet to see a band who can top them in terms of sound quality.

Best: Megadeth, Pearl Jam, Meshuggah, Black Label Society

Worst: Hoobastank, Velvet Revolver

Best, oh so many but I'd have to go with Jethro Tull in 1974, War Child tour, Portland

Worst, easily Aquarium Drunkard » Sevens: The Replacements – Portland

Best: Black Sabbath, Vector Arena Auckland, NZ

Worst: The National, Vector Arena, Auckland NZ (not that the band sucked, they were fine - the sound was ****, the lighting terrible, venue way too big)

Best: "Weird Al" Yankovic