If you send a lot overseas and really do want tracking, look into DHL ecommerce (GM packet).

It's an economy service, so delivery timeframe is about 2-4 weeks, and it costs you $11 for each pick-up if you can't drop off, but you should be able to send a fully tracked package containing a CD to the US for about $10, depending on the contract rates you're given, which is less than half what it would cost through Aus Post.