Below are rotatable, zoomable, pannable three-dimensional models designed to be used for drawing practice. 
Primitive Forms
The basic building blocks to construct more complex forms.Cube
Three-dimensional form that you can rotate and draw.
Randomized Cube
Three-dimensional form that you can rotate and draw.
One Way To Construct A Rotated Box
One way to construct rotated boxes, This model was inspired by this YouTube video.
Sphere
Three-dimensional form that you can rotate and draw.
Circles And Ellipses
A simple circle in three-dimensional space, drawn with helpful construction lines.
Flattening Planes, Circles
A simple circle in three-dimensional space, rotated in various degrees. Based on the flattening planes warm-up suggested by Brokendraw.
Flattening Planes, Squares
A simple square in three-dimensional space, rotated in various degrees. Based on the flattening planes warm-up suggested by Brokendraw.
Cylinder
Three-dimensional form that you can rotate and draw.
Cone
Three-dimensional form that you can rotate and draw.
Equilateral Triangle Pyramid
Three-dimensional form that you can rotate and draw.
Pyramid
Three-dimensional form that you can rotate and draw.
All Primitives
Choose this model if you just want to practice all primitive forms: the box, sphere, cylinder, cone, and pyramid.