The publisher of the German computer magazine "c't", Heise, is doing a listening test of various lossy audio formats at 64 fixed and ca. 128 vbr kbps. Mp3, mp3pro, aac, ogg, wma and real audio are to be tested. Everybody can participate. You have to register for a temporary account to download the test files (wav or shorten); 7 in total, one as reference. Your object is to sort these from worst to best sounding.

More info here (German):
http://www.heise.de/newsticker/data/vza-22.08.02-000/
http://www.heise.de/ct/leserbefragung/hoertest/
The survey ends on the 29th of August. Have fun!