Here's a picture of a woodspirit I carved out of cottonwood bark. I feel like this one came out pretty well. The composition is good, the finish came out well, and the contrast between the inner bark and outer bark is very pleasing.
Cottonwood bark is an incredibly enjoyable material to carve. It's like carving thousands of sheets of compressed newspaper. You still want sharp tools but the it's much easier on my hands. I purchase my cottonwood bark from a gentleman in Montana. The western bark is usually thicker and comes in larger pieces.
This piece was old through Turning Leaf Wood Art Gallery in Blue Ridge, GA. The books I have listed below have some good examples of cottonwood bark carving.