Most practical advice I've seen in this thread. For anyone who wants to protect their hearing at a concert without making the music sound muffled, check out these flat frequency ear plugs:
Those are great but I recently switched to these. They are a little more expensive but they come with three different filters for different decibel levels.
Please wear them at shows. Coming home with your ears feeling like you are underwater and ringing is a sign you've damaged them. I don't know why they insist on making shows so damn loud.