I've tested most MP3 players and found mpegToaster to be the best solution for minimizing CPU without sacrificing too many features. It takes only 1/3-1/4 the CPU time of iTunes (test on a 266MHz G3 and 1GHz G4) but can still use iTunes' play lists. For me, this is great time saver, since I use iTunes to rip, organize, and sync with my iPod, but don't want to use it to actually play MP3's. Moreover, mpegToaster is optimized for AltiVec, while mpg123 is not, which makes it THE fastest play on G4's. That said, it could use a few more features, such as: an equalizer (which Mu has), a sliding bar to move into the middle of songs, and a smaller player (only) footprint to which it minimizes.