The Ad Council is a non-profit organization that produces public service announcements (PSAs). Among its successful PSA slogans are "Loose Lips Sink Ships," "Only You Can Prevent Forest Fires," and "Friends Don't Let Friends Drive Drunk."

Includes print, TV, and radio ads. Most ads are from 2000 or later.

A non-profit organization that rates ads on their portrayal of LGBT themes. They host a large archive of print ads and TV ads, covering the 1920s up to the present. The archive can be useful for any ad-related research, not just research into LGBT themes.

A collection of TV commercials from the 1950s - 1980s, provided by Duke University Libraries.

A collection of classic TV commercials, mostly from the '50s and '60s, hosted by the Internet Archive.

An archive of TV commercials from US presidential campaigns, from 1952 to the present. Provided by the Museum of the Moving Image.

A well-organized collection of tobacco ads. Includes both print ads and TV ads. Provided by the Stanford School of Medicine.

YouTube is perhaps the best online source for commercials. Try combining your search terms with the word "commercial" or "ad" or "advert" or "advertisement."