Faxmonkey did it on PTR. Dezu did it on live. I did it on live and frapsed it. This isn't the same as Faxmonkey's video as his method wouldn't work on live. If you want to solo Onyxia on live as a mage, or just see it done by a mage before 3.0.8, go watch. =)
Envy - Fahrenheit
Disturbed - I'm Alive
Bobby - She's History
Billy Idol - Dancing With Myself
Digital Explosion - Story Of Snowman And Sunshine Girl
Scarface Soundtrack - Push It To The Limit
You can read about the tactics at http://forums.wow-europe.com/thread.html?topicId=7539774573&sid=1 or at http://onyxia.enquillion.com/ whilst downloading..