Here's an interesting MP3 bit rate chart including 'comparison' sample clips using the song "Smooth", by Santana:
http://www.bellaonline.com/articles/art17931.asp When attempting to rip the highest quality (most accurately reproduced) MP3's possible for playback on my iPod, I use & recommend "Exact Audio Copy" EAC:
http://www.exactaudiocopy.de/ It's better than the rest, and believe it or not, it's 100% free as well.
I rip at 192 kbps as I find this produces the best results with minimum tradeoff in quality vs compression.
Scott