There are many fantastic websites dedicated to vexillology (the study of flags) and the history of heraldry. We will continue to add links to those resources. Please contact us if you would like us to add a link to your website or resource.
Flags of the World website - Huge resource maintained by volunteers from around the world
Vexilla Mundi - Another great resource. Provides dimensions and PMS colors for flags.
Heraldry of the World - Specific to heraldry. Detailed, well organized and informative.