d20 isn't old school, of course. But these freebies have good content that is easy to adapt to most OSR rulesets.
Rather than point you to each archive.org link, I've thrown them all in a folder on my DropBox account. Feel free to download to your heart's content. I'll probably be yanking these in a few months to free up the space.
If anyone has any other non-WotC freebies from the d20 era that I should throw in the folder, let me know.
EDIT: Link & files removed on 2015-03-05. I figure if you haven't grabbed them by now, you aren't going to, and I need to clean up space in my Dropbox account.