Sound Cruising
Shimokitagawa is an area in the west of Tokyo. I think it's fair to call it the Camden of Tokyo: densely packed streets, flea market, hundreds of second hand shops, and a vast array of live music veues ranging from the smallish to the minscule.
Shimokitazawa Sound Cruising is an all day music event where 18 different venues have live music from 11am until 5am (when the metro starts running again). We went to check it out. We did not stay till 5am :)