modest mouse. i've seen them twice, because i'm stupid and stupidity is doing the same thing twice and expecting a different result. the first time, they were dull, lifeless, and the sound was so bad that i left early. the second time, the sound was ok, but they were still dull and lifeless. then the flaming lips came on and kicked their asses back to the stone age. the flaming lips were awesome live, i don't know what that other poster was tripping on (or maybe he wasn't, and that was the problem).
but modest mouse is one of my favorite bands on CD, i have all their albums and love them to death.
other bad live bands: deftones (OMG they are so bad live), RHCP, blink 182, alkaline trio, the appleseed cast, the mars volta (sorry, 30 minutes of guitar feedback and tight pants is not a show).
great live bands: portishead, tool, radiohead, thursday, smashing pumpkins. sigur ros, dave matthews band (not a big DMB fan anymore, but no denying they are a solid live band)
keep in mind i don't expect bands to sound like they do on the album. if you know anything about making albums, you know it is impossible for most bands to replicate the CD by themselves live, but that doesn't mean it sucks, just that it's different and you need an open mind for a new experience
edit: i saw incubus touring on make yourself and it was a solid set, they blew away the deftones. they have really gone downhill IMO though.