The Levelator is my new best friend.

"So what is The Levelator®? It's software that runs on Windows, OS X (universal binary), or Linux (Ubuntu) that adjusts the audio levels within your podcast or other audio file for variations from one speaker to the next, for example. It's not a compressor, normalizer or limiter although it contains all three. It's much more than those tools, and it's much simpler to use. The UI is dirt-simple: Drag-and-drop any WAV or AIFF file onto The Leveler's application window, and a few moments later you'll find a new version which just sounds better."  (bold type is mine)
http://www.conversationsnetwork.org/levelator 

It is FREE and it works wonders.