Papercraft Sites:

Has a neat collection of Mario and Donkey Kong models.
Large collection of crafts from Zelda and Mario.
Zelda, Animal Crossing, Starfox, Banjo-Kazooie and more!
One of the most prolific designers on the internet. Huge archive and very high quality.
The best site for Nintendo themed models. Gathers crafts from the web, as well as models from their own designers.
Extensive user-friendly archive of a wide variety of models.
A large and ever expanding archive of all types of papercraft available on the internet.
If a model exists on the internet, then it's probably listed here! Massive constantly updated archive.
A very productive and skilled team aiming to eventually create a model of every single Pokémon!
Long running site containing models from almost every single Zelda game!
Regularly updating blog with content from Mario, Pokémon and Zelda.

Useful Resources:
Developers of the unbelievably useful software for creating papercrafts! Also functions as a very helpful 3D guide for unfolded models! Download the viewer for free if you can (PC only). You'd be silly not to!
One of many programs available that allow you to open RAR archives.
Papercraft Museum's helpful video guide to get you started.
An in depth guide to perfecting your builds and designs.