I was at the recent Live at Hammersmith release from The Darkness... can't think of any other music ones, but I'm somewhere in the crowd for Bill Bailey's Part Troll if that counts. There was a bit of Slayer in there I suppose!
This all pales next to my Dad's efforts as he was present for Genesis Live, IOW festival 1970, Queen at The Rainbow '74, and Deep Purple Live In London - the hooligan yelling 'Smoke on The Water!!' - that's him.