One of the best ways to learn about mesh topology is to study what others have done. I've created a small collection of images showing the topology for use as reference. For a more in-depth understanding of topology consider checking out my most recent book that covers digital modeling or the free article I wrote on the subject for HDRI3D, "Go With the Flow".
100 Character Models
The video to the left was released online several years ago and showcases 100 character models that I created, revealing their topology. A higher quality version can be downloaded by clicking this link: