You can find free and paid 3D models in .obj and other formats at these websites:
CGTRADER - diverse types of 3D models
GRABCAD - diverse types of 3D models
HERMAN MILLER - limited to model types usually not directly usable in Blender, however you can convert them from .skp and .dwg . They used to have 3DS formatted models there, which could be brought into older versions of Blender directly, but I don't see them there now, and with Blender no longer able to do .3ds imports, I guess they won't be missed much?
KOHLER - Free 3D models of thousands of plumbing fixtures and bath related products in .obj and other formats.
TURBOSQUID - diverse 3D models
SKETCHFAB - diverse types of 3D models
I am creating a new free model download page at avuvi.com, the first model set is now there.
Recycled Plastic Trash Receptacles (AKA Trash Bins or Garbage Cans :^) I figure if you're going to start anywhere, start at the bottom. These are great for parks, campus sites, camping sites, housing developments and public areas. They are to scale, and the recycled is an original procedural texture I came up with.