Audacity or any simple sound editor?
 

Something I can do things like edit commercials out of MP3s, or perhaps transcode to a different bitrate?

I don't need everything Audacity does, but it would be nice to edit.

Re: Audacity or any simple sound editor?
 

sox?

Doesn't deal with mp3s by editing at frame boundaries and such, but works good if you can accept re-encoding loss.