Zio Prudenziati was apaper model designer genius from Italy. The model designs he left us are available for free.
Curell graphics has quite detailed models of the Concorde, Spaceship one, Airships and ships.
Vinicio Lucas Vargas has really nice free models mainly of Brazilian Aircraft.
The Lower Hudson Valley Paper model giftshop has great models, mostly of both real and fictional spacecraft and aircraft.
Hollo Papirmakett very nice hungarian site. The text is in hungarian language, but the interface is easy enough to understand without knowing the language.
skyscrapermodels has a great series of models of the tallest buildings in the world by John Townsend
Ninjatoes does a lot of figures models including highly upscaled LEGO minifigs and also has great Star trek models. If you visit his site, make sure to check out his links collection.
paperdiorama.com has public transportation models, like busses and a subway train. The site requires free registering to download
Spitefuls has lovely disaster dioramas.
The Papercraft museum is a huge collection of free papercraft from all kinds of categories.