Braintree (a payment processor I use and highly recommend) has a number of resources (videos, articles, etc.) at their blog (http://www.braintreepaymentsolutions.com/blog). Look on the left-hand side for the PCI-specific resources, or use the search bar on the right for their blog archives.

You can start reading at https://www.pcisecuritystandards.org/

PCI is, just like most other certifications, like a pyramid scheme. Except you don't get a piece of the pie :-)