It's amazing what videos you can find on YouTube. I've been searching on youtube and some cool Space Mountain videos have been recently added.
http://www.youtube.com/watch?v=FdQVpcYcm64
Space Mountain before the 2002-2005 refurbishment (no music though).
http://www.youtube.com/watch?v=P-tT30PCPAk
Hong Kong Disneyland's Space Mountain with excellent music quality!
http://www.youtube.com/watch?v=l1Hx6N48Q50
Tokyo Disneyland's old Space Mountain
And...saved the best for last!
http://www.youtube.com/watch?v=Q3PUecp-OSw
Disneyland's Space Mountain...THE WHOLE RIDE LIGHTS ON!