When I was a heavy 3d object user (mostly for rendering purposes) I was a Formfonts subscriber:
http://www.formfonts.com/index.php?area=1
For a flat annual fee you get a lot of very good models in various formats, including 3ds and Sketchup.
What I found out was the quality of the models (textures, geometry and low polygon count) and the sheer variety of them more than made up for the annual fee (around 200$ year, if I remember).
My favorite workflow was to convert them into Artlantis objects, where I did all my renderings.
