Very large noncommercial source on vexillology. Searchable database, glossary, bibliography, and related links.
  http://www.crwflags.com/fotw/flags/  [Site Details]

Pictures of current and past national and state flags. Includes flags of the Revolution, the Confederacy and possessions and territories.
  http://www.law.ou.edu/hist/flags/  [Site Details]

Printable version of each of the 50 US state flags. Includes description of each.
  http://www.50states.com/flag/  [Site Details]