TinkerCad is a web-based 3D modeling program. This free to use program offers tutorials that will help you learn the program and be able to create your very own 3D models.
The NIH 3D print Exchange contains various 3d models of biological items. These include molecules, anatomical features, cells, and even lab supplies.
MyMiniFactory is a 3D model database with a large selection of models sorted into categories, including educational