Earplugs for concerts?

Any suggestions for noise-reducing earplugs that are good for concerts and other loud music? Ideally, I'd like something that lets through all frequencies equally, while reducing the noise level by some number of decibels.

Who makes these?
Etymotic Research: http://www.etymotic.com/ephp/erme.aspx
If you don't want to spend the money for custom earplugs these Etymotic ER20's work pretty well.
I've used both suggestions listed above - either is a good choice!
The Etymotic ER-20s work very well.
Awesome. That's exactly what I was looking for. Thanks, folks!
Just bookmarking this for future reference.