In this job, I get to try out a lot of cases, and they're usually plastic, metal, rubber, or fabric. But the Q Card Case for CM4 is an interesting hybrid, combining a soft leather-like fabric where it counts and rubber for the phone case component. They have even applied for a patent for this combination.
The fabric portion has a slot that can hold up to three credit card or ID cards as well as some cash. There's a nice slot that makes it easy to eject the cards as needed.
The phone case portion covers the front glass nicely, which many cases don't do. This gives your phone some added protection when the phone is placed face down.
The case I tried was black, but CM4 will have more colors, including a white model coming out soon, that would look great with a white version of the iPhone 4S.