Need a Favor: Serious Question for all you DM's Out There

I'm doing some market research.

If you've got the time, could you give me a quick list of your top 10 favorite OSR products? Not counting rule-sets? For pay or free.

It's ok to list less than 10, if you would prefer.

Either a blog post, or leaving info in the comments here would be fine, though I would appreciate it if you dropped a quick comment to let me know you're making a post of it. Just to make sure I don't miss anything.

Thanks a million!