Delta 7 Studios has a collection of free paper models of the Seven Wonders of the Ancient World: the Great Pyramid of Giza, Hanging Gardens of Babylon, Temple of Artemis, Statue of Zeus at Olympia, Mausoleum of Maussollos, Colossus of Rhodes and the Lighthouse of Alexandria.
Dungeoneering dot Net has a nice selection of printable terrain tiles ostensibly for use with the Dungeons and Dragons miniatures game, but which would also work with any number of dungeon crawl games — of which there are many free ones available on this site.
The Paper Model directory has a collection of links to dozens of paper car models, from DeLoreans to Hondas. These are just what you need to populate the streets of your modern era miniatures wargames. As is usual with these, you can use your printer settings, graphics program (that’s what I use) or a copy machine to adjust these to whateve scale you need.
The Independence War Paper Models site has some very nice — and free — paper models of starships.
Germy’s World has a paper model for making your own dungeon, but what is more interesting is Victorian Cellar model that accompanies it. It’s perfect for gothic horor games as the lair of a monster, or mad scientist or cult.