Hawkwind (no surprise, eh?) Electric Tepee tour, 1992, Brighton. I think it was the second night of the tour, and a friend and I had gone - we were somewhat disappointed when they came out as a three piece, expecting a lacklustre performance. Then the opened with Right to Decide off the album, which we'd never heard, and within seconds we were blown away - the sound was amazing, they were incredibly tight and seemed to be enjoying themselves immensely, and the song was catchy as all hell.
The rest of the gig was great, but the first minute or so was mind-blowing.