"Historical Resources on the Internet" -- This page is no longer maintained (so some links don't work) and is only accessible now from the Internet Archive, but it is still one of the best and most comprehensive lists of online historical sources I've ever seen. [NOTE: For broken links, try searching for the title; chances are, the collection's just moved.]
CNN Video Almanac -- "We've collected our best video since the birth of CNN in 1980 [up to 1997]. Choose a year or topic below to begin a multimedia tour through history." See the companion sports version here: http://www.pinterest.com/pin/328622104031902777/ [Screenshot 20140218.]
"Broadsides and Ephemera Collection" -- Duke University Libraries -- Has 5500 "...broadsides, pamphlets, form letters, posters, newspapers, tickets, & other short printed items" from the 18th to 20th centuries (mostly 19th). Includes "materials related to political campaigns, politics, theater, dance, popular entertainments, immigration & emigration, advertising, travel, expositions, military recruitment & campaigns, as well as issues related to race, class, gender, & religion."
"Online Speech Bank: Database of and index to 5000+ full text, audio and video versions of public speeches, sermons, legal proceedings, lectures, debates, interviews, other recorded media events, and a declaration or two." Special feature: "Top 100 Speeches: Full text, audio, and video database of the 100 most significant American political speeches of the 20th century..." [Screenshot 20140215 via Pinstamatic]