NPR has a great audio quality comparison test
NPR has an amazing quiz for various bitrates of compressed audio. It will test to see if you can hear the quality difference three different bitrates: 128Kb/s, 320Kb/s, and uncompressed. I've taken the test several times and I'm unable to hear the difference for anything above 128Kb/s. I even used headphones to get the best experience and it didn't help.