I love model sheets, as those of you that have taken my Illustration courses may already know. They are such a good example of creating a believable and reproducible character by asking yourself what they look like from all sides and how they move and how their faces move.
I just found out that Cartoon Network is relaunching an 80s favorite, the ThunderCats. Here is a sample of the model sheets:
Here are some additional links to collections of model sheets: