Technically, I saw Lifehouse live at the California State Fair like ten years ago. But I only knew one song by them and we weren't even in the stadium, we were just walking by, so I'm not gonna count it.
My first real concert was Relient K, opened by Owl City (before they were famous) and Runner Runner. The opening bands were... alright, I suppose, but Relient K was excellent. I gained some new favorite songs of all time that night, and my friend made a CD that had every song they performed, so that ruled.