From its long history of launching rockets and operating spaceships, NASA has posted a big collection of sound-clips that are suitable for ringtones, computer warnings, etc. : NASA’s stream on SoundCloud

Here’s a collection of NASA sounds from historic spaceflights and current missions. You can hear the roar of a space shuttle launch or Neil Armstrong’s “One small step for (a) man, one giant leap for mankind” every time you get a phone call if you make our sounds your ringtone. Or, you can hear the memorable words “Houston, we’ve had a problem,” every time you make an error on your computer

(There is also this page at NASA: Connect Sounds – NASA.)

Here’s a sampling: