Hawkwind, Chrome, X/The Knitters (even though they’re kinda phoning it in nowadays), and the Damo Suzuki Network are all much better live.
mum is great on CD, but put on one of the most boring live sets I’ve ever seen.
Counting Crows. They are nothing short of horrible live. Nothing short of horrible.
Genesis is just awesome live. Even songs of theirs that I don’t like are good to listen to live.
From what I’ve seen on Youtube and DVDs the Beach Boys were horrible live. Although I saw Brian Wilson in concert last year and he was surprisingly great.
Aerosmith’s studio version of Train Kept a Rollin’ is boring as shit, but the live versions are amazing.
Gomez is great on the radio, crap in person.
Lindsey Buckingham is amazing live, studio I can take or leave.
He’s amazing in the studio, too - just applying a different toolset (production skills) vs. live (playing skills). Deeply talented guy.
Tori Amos is an amazing live performer, while her last few studio albums tend to be dull. I enjoyed listening to her last album, American Doll Posse, until I was able to download songs from her last tour off of ITunes. Once I started listening to the live songs, I can’t listen to the album anymore, its just too controlled and slick. There are certain albums I have no problem listening too (Boys for Pele, The Choirgirl Hotel) but the rest I have to hear live.
While I love ZZ Top’s recorded music with regards to the quality of songwriting and skill as musicians, seeing them live just brings a whole new element of cool to the experience.
If no one wants you to leave the stage so the Stones can come on, your performance is waaay beyond badass.
They’re not just from Texas, they are Texas.
Bob Dylan. I’ve been to 3 of his concerts over the past 20 years or so, each worse than the one before. He doesn’t give a crap about his performance, he doesn’t engage with the audience at all, he doesn’t acknowledge his backup, he makes no attempt to sing clearly at all. As talented a writer as he is and as much as I enjoy his CDs, I honestly have no desire to see him again.
I heard that while the Barenaked Ladies are great on album, their concerts are absolutely godly. Though that may have more to do with the banter they do in between songs than the music itself.
The Pixies are fantastic in the studio, but I’ve seen them twice live and they are crap, junior-high-talent-show bad. I’m amazed that their live performances didn’t destroy all of the indie-rock credibility and fame that they had.
I saw them last summer with Steve Winwood opening. One of the best concerts I’ve ever been to. Steve got back on stage later so they could all sing “Gimme Some Lovin’” together. The entire audience was on its feet going crazy. It just rocked the entire venue.
If that happened to be the Summerfest concert, I was there as well and it was my, I believe, 7th TPATHB concert. Funny thing is, I got dragged to the first one kicking and screaming. I didn’t like Tom Petty in much the way some people don’t like Bob Dylan. I walked out absolutely amazed, and now I never miss him if he’s in Milwaukee (or even Chicago or St Paul).
No, this concert was in Virginia (Nissan Pavilion); I don’t think it was Summerfest, anyway.
If he comes back around, I will definitely be getting tickets again. I’ve liked TP since I was in high school (79-83), but that was the first time I saw him live. I was completely blown away by his performance.
I got a couple pictures of the concert here (not the greatest, but you can get the idea). 
Sonata Arctica and Rhapsody (now Rhapsody OF FIRE !) were both notorious for being absolutely horrendous on stage. Sonata’s gotten better though, last time I saw them I didn’t have an urge to strangle the guitarist with the singer’s voice box.
Iron Maiden is far better live - these days I barely listen to their non-live albums anymore. Seeing them on-stage was just… ROOOOAR ! 
I thought Led Zepplin blew chunks live. Too high to perform well.
Dream Theater is one band that sucks live. Labrie squawks and falls way flat, not to mention how rigid everyone is on stage. That said, in the studio they are (contrary to popular opinion :p) fucking awesome.