3D Resources

GAC is in early alpha - it's a minimal version of what it should be. As such, it ships with a very minimal set of 3d models. When you run GAC for the first time, you can import your assets before models appear in the resources widget and can be drag & dropped into the main scene.
Use either the import button, or open the assets directory and link your assets in it. Pro-Tip: you can import a whole folder at once.

Links

The following sites are good resources to get free & paid 3D models:

and much more!