Songkick seems to be the most reliable source now for finding out about gigs in a large number of places worldwide. To me, their site seems clunky and unintuitive, though their synchronisation with other sites is pretty impressive.
Last.fm have been doing exactly the same thing for a hell of a lot longer, and their events management seems to be just as bad, but by allowing anyone to add an event instantly, they were the go-to source.
I always think Last.fm is such a useful tool, with a wealth of listening data from a huge number of users, but to me it seems like there's so much more they could do but never have. I'm guessing it's when CBS Interactive bought it that it went wrong, but don't have a clue really.