Classical Pontiac http://www.classicalpontiac.com/ - Their web site contains a classified listing for cars and parts for sale and a place to post parts wanted. Great site and the reason we were reluctant to build another classified section on the web.
Hemmings Motor News http://www.hmn.com/ - Find their catalog on the news stand to help find Firebirds for sale, Firebird parts dealers, or almost anyone that has anything to sell. Their web site also has the best club and car show database.