I am VERY excited about this site!
Let the intro page of SpaceSounds.com run for a few minutes and you'll hear a short history of humanity's steps into space. The actual site (click on SpaceSounds logo) contains both natural and manmade sounds.
I've only been able to listen to some of the sounds available from this amazing site. The download times are long, but more than worth it....
Some sounds include:
Two pulsars that rotate at different speeds
Communications from Gemini, Mercury, Apollo, and Shuttle missions
Tell your friends, especially the teachers!