Stamps.org - The official webpage of the American Philatelic Society
USPS: Stamp Collecting - The US Postal Service stamp collecting website
USPS Stamp Store - Purchase stamps here!
Postal Museum - The Smithsonian Postal Museum offers stamp collecting resources and more!
Starting a Collection - Information on how to get started collecting!
Stamp Smarter - A great website with resources, stamp look-up tools, and more!
Stamp World - A comprehensive online catalog of stamps around the world