Here's a sketchbook from Mike Corriero, a freelance concept artist and illustrator who has worked with many big name clients and have his work featured in multiple art books and magazines.
This 68-page collection features lots of designs for creatures, alien life forms and a bit on environment. These are pen/pencil black and white sketches. The concepts look really cool and have nice details. They range from alien bugs to flying dinosaur-like creatures.
You can order this sketchbook at Lulu.com.