I'm not sure where they came from, but I stumbled upon a blog where you can download some incredible outtakes from Pink Floyd's Dark Side of the Moon recording sessions. It's also got this video with some hilariously dated interviews.
For that matter, this site has an alternate version of the entire Dark Side of the Moon album available for download.
And there are more demos and outtakes available here for download.
I won't lie: I love the Internet.