Mac OS X Hints has an interesting post about how to rip just the audio from DVDs. I've only really had to do this a couple of time, but when I get a chance I'm going to test out some new methods.
They cite this method, which uses Mac The Ripper to rip the AC3 audio and then ffmpegx to transcode it to mp3, but the apps are a bit long in the tooth (ffmpegx's last update was January 26th 2008) or a bit tricky to get a copy of a recent version.
An alternate to ffmpegx is MAC3dec but that's a bit of an old app as well. Apparently last updated on August 26th 2004.
Mpeg Streamclip is probably the best way to go that I've seen so far.
(Yes there's OSex but it's pretty old.)