We first wrote
about The Levelator
when it was just a wee app in beta, but now it is all grown up and has hit version 1.1.0. The Levelator, as you might recall, can take an audio file and automagically adjusts the levels so everything has the same base level (though some things are louder than others, as it should be).
New in 1.1.0 is an entirely new (and very un-Mac like) user interface, as well as a new license that permits free use of The Levelator for commercial projects (the previous license only permitted free personal use).
The Levelator is Univeral, requires OS X 10.3 or later, and is free.