Default Models
This is a simple addon that brings iconic 'benchmark models' to Blender! Access these in the add mesh menu:
Shift + A

In the spirit of the history of these models, this addon is of course free :)
The Utah Teapot features areas of positive, negative, and zero curvature. I'm told it comes default in Houdini, Lightwave, and 3ds Max.

The Stanford Bunny is probably the most iconic model from the Stanford 3d scanning repo. Used in basically every kind of demo (physics, raytracing, segmentation, etc).

The Stanford Dragon is usually shown in raytracing and rendering demos due to it's geometric complexity. Also the most badass of the 'legendary models'.

Finally here is the whole crew posing:

Enjoy and use them in all your demos - I know I will!