A while back, I took a look at Levelator (from the Conversations Network) and it was a bit rough around the edges. It's a tool that take an audio conversation like a podcast and evens out the audio levels of the different speakers. This is no easy trick. I normally spend a while on this with every podcast we produce. I've still had comments that sometimes my voice is almost deafening but the guest is a bit quiet. I've found the main problem is that people you interview vary their amplitude enormously at different parts of the interview.
Today, I pulled down the latest version and tried it and have to say I love it. You'll see the effect of it in the latest SQL Down Under show (ie: show 43). The interface for selecting files, etc. is still a bit funky, there don't seem to be good options for naming input and output files and I'm surprised it doesn't deal directly with mp3 files (I converted to WAV via Audacity before using it) but the effect that it produces and the cute screen animations are both excellent.
We're now going to go back and "levelate" all the previous shows. This should improve them quite a bit.
Highly recommended! And even better, free!