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.
The Alternate Realms site has several nice cardstock buildings, including some huts and a chapel. The page also has a couple of tanks and a science fiction walker vehicle. Finally, there’s a model of St Michaels tower on Glastonbury Tor (sp?).