I saw In Flames in 1999 on the tour for COLONY at a really small venue in Toronto called the Kathedral, probably only a few hundred people there.
Mr. Bungle on their last tour in 1999.
And although I'm not too proud of it I've seen bands as opening acts only for them to become MUCH bigger than the bands they were opening for. Incubus and Finger Eleven opening for Primus come to mind.
08/23 - Alice in Chains
09/19 - Deafheaven
10/18 - King Diamond
11/01 - Suffocation
12/06 - Distant Worlds: the Music of Final Fantasy