Popular resources on the Payment Card Industry Data Security Standard, including links to the PCI DSS standard, and the PIC Security Standards Council:

Payment Card Industry Security Standards Council

Payment Card Industry Data Security Standard (PCI DSS)

Changes from PCI 1.0 to 1.1

VISA Cardholder Information Security Program (CISP)

Mastercard Site Data Protection Program

Discover Information Security and Compliance (DISC) program