Free Stuff

DriveThruRPG has a large free section. Free is good. This isn't an endorsement of the site. It's an endorsement of free.

Want some free miniature rules because you want to try something new?
Heavy Gear Blitz Rulebook

Looking for a way to test out a new miniature but don't want to pay for a bunch of new minis?
15mm Paper Miniatures

Terrain?
Paper Buildings

Remember BESM? Here are the core rules if you want a quick easy to learn flexible RPG.
Tri-Stat Core Rules

In the late 80's and early 90's there was a Star Wars RPG by West End Games. Here are the core rules now available for free. Don't miss the links at the bottom for even more free D6 files.
D6 Core Set Bundle

Free Paper Terrain Files

Why because free is good. I found these when surfing the internet in a place I didn't expect. While intended for fantasy games you could use them for just about any kind that involves miniatures.

http://www.wizards.com/default.asp?x=dnd/fpm/archive