The Prelinger Archives (ht

The Prelinger Archives (http://www.archive.org/details/prelinger)

Footage Firm (http://www.footagefirm.com/freeclips.asp)

There are more but these two have the most (especially Prelinger).

You can also find good stock footage for reasonable prices (like when Digital Juice runs a special on their VideoTraxx – I bought all three volumes for under $400 combined – over 100 DVD’s filled with RF footage).