Hawks Wargames has a large selection of downloadable 10mm full color paper model science fiction buildings.
Here's a paper model of an ancient Central American style temple, just ripe for sacrifices. I think it would be terrific for a pulp action game.
There are just too many good 2.5D fantasy miniatures on Eddnic's site to begin to list them. Visit and take a look.
Greywolf offers a large selection of paper models of post-apocalypse style cars scaled for 15mm/20mm as well as a few designed for 25mm / 28mm. Scaling the figures with a printer should not be a problem, though.
Nintendo Papercraft offers some slightly cartoony looking paper models of palm trees.