I'm scheduled to take the CMSRN on Feb 27th. I'm so nervous!
I took a 10 week course offered through a local university that my job paid for. It was pretty intense and covered all the systems and then some. The books they recommended were the ones on the AMSN website. They are both very informative. I can see referring back to them again and again.
Others that I know have just used NCLEX to study with and others have hardly studied at all.