Here are some downloadable houses (with some new links and dead links removed):

Christmas house templates but they can obviously be decorated any way your like - they are sooooo cute!

Cute little bird house template to download as a PDF here

This link has houses but also a variety of roofs that may work with other designs as well

Adaptable "kids craft" house at DLTK

Easter Egg cubby house here

Cutesy printable here

Sweet little ornament here

Cute townhouse gift box and a glittery one here ( a How To article) at Martha Stewart

Scor-pal houses

Template from The Barefoot Stamper - scale up to the size you want.

And my own personal favourite - not 3D but fab little wonky houses from Dan99