An OpenCart beginner's guide book is availble for pre-order £36.93 ($63.18 USD).
Here is the description:
Develop a professional, easy-to-use, attractive online store and shopping cart solution using OpenCart that meets today's modern e-commerce standards.
Easily integrate your online store with one of the more popular payment gateways like PayPal and shipping methods such as UPS and USPS.
Provide coupon codes, discounts, and wholesale options for your customers to increase demand on your online store.
- With hands-on examples, step-by-step explanations, and illustrations
You can purchase the book here:
There is also another book on its way about developing templates for openCart.