For Flag Design
Online flagwaving simulator—great for testing out designs
Canadian Heraldic Authority—The Public Register of Arms, Flags, and Badges of Canada
Flagmaker & Printer—design and order your own flag
My Own Flag—a guide for elementary-age students
Vexillology Wiki—see and post flag-design proposals for countries and states/provinces
Modern Flag Design—an expansion of 'Good' Flag, 'Bad' Flag
If you find a good resource to add to this list, sent the website link and a short description to the Secretary.