Anytime you write a letter, you use the ZIP code. What is that code, and when did people start using it? More importantly for the postal service, how do you get an entire country's population to memorize and add a seemingly random string of numbers to their addresses?

The answer, in the 1960s, was Mr. Zip, a jaunty cartoon postman, designed to make the new ZIP code cause memorable and approachable.

This website discusses the ways in which Mr. Zip was deployed as an educational and advertising device. The majority of the content consists of an essay divided into smaller, more manageable subpages. However, sprinkled throughout, you'll find Mr. Zip comics; merchandise, such as board games and lunchboxes; promotional materials; PSA videos; a memo; photographs; and postage stamps.

This video describes what each number of the ZIP code represents, which could be a hook if you decide to introduce Mr. ZIP in the classroom. Ultimately, the content is not likely to be of direct use in the classroom but may be of more interest as trivia or to flesh out background knowledge for related lessons.

This website offers brief articles on roughly 65 topics within Minnesota history. Each article in turn consists of text, images pulled from the Minnesota Historical Society, a bibliography, and a list of references (divided into primary, secondary, and web resources) for those interested in further information.

The content can be filtered by category (such as event or structure), topic (from "African Americans" to "women"), or era, making it easier to find items of interest.

Currently, the site is in beta testing. The Minnesota Historical Society invites comments from all site users, and plans to greatly expand the number of available articles throughout 2012. In the meantime, there's a wealth of information available ranging in content from the oldest sauna in the state (and most likely the country) to a major 1800s African American newspaper.

This collection presents 1,395 photographs by the American photographer, music and dance critic, and novelist Carl Van Vechten (1880-1964). The site consists primarily of studio portraits of celebrities, most of whom were involved in the arts, including actors, such as Marlon Brando and Paul Robeson; artists, such as Marc Chagall and Frida Kahlo; novelists, such as Theodore Dreiser and Willa Cather; singers, such as Ethel Waters and Billie Holiday; publishers, such as Alfred A. Knopf and Bennett Cerf; cultural critics, such as H. L. Mencken and Gilbert Seldes; and figures from the Harlem Renaissance, such as Langston Hughes, Countee Cullen, and Zora Neale Hurston.

More than 80 photographs capture Massachusetts and Maine landscapes and seascapes; others include eastern locations and New Mexico. Many photographs of actors present them in character roles. Searchable by keyword and arranged into subject and occupational indexes, this collection also includes a nine-title bibliography and background essay of 800 words on Van Vechten's life and work. A valuable collection for the documentation of the mid-20th-century art scene.

Featuring texts by and about Martin Luther King Jr., this regularly updated website currently contains more than 1,400 speeches, sermons, and other writings, mostly taken from five volumes covering the period from 1929 to 1968. (These are listed in the Published Documents section under Papers.)

In addition, sixteen chapters of materials published in 1998 as The Autobiography of Martin Luther King Jr. are available. The website presents important sermons and speeches from later periods, including "Letter from a Birmingham Jail," the March on Washington address, the Nobel Peace Prize acceptance speech, and “Beyond Vietnam.” Additional materials include an interactive chronology of King's life, two biographical essay, over twenty audio files of recorded speeches and sermons, and twelve articles on King. More than thirty photographs complete the website.

The King Papers Project is valuable for studying King's views and discourse on civil rights, race relations, nonviolence, education, peace, and other political, religious, and philosophical topics.

Four guided investigations designed to teach students how to read primary sources and construct historical narratives lie at the heart of this website. Topics are: the Spanish-American War, the Scopes Trial, Social Security, and Rosa Parks. Each topic includes a short introductory video, a timeline of events, a central question, and extension activities. For example, the Rosa Parks investigation poses the question: "Why did the boycott of Montgomery's buses succeed?"

After completing a simple login, students read annotated documents—including letters written by the boycott organizers, a speech by Martin Luther King, Jr. and an interview with a woman working in Montgomery—and answer guiding questions, and draw on their responses to answer the question. The website also includes a useful introduction to the idea of historical thinking.

Developed primarily to support a PBS film, this website uses Twain's writings to illustrate his life. An interactive scrapbook, similar to the one patented by Twain, is the centerpiece of the site and provides access to nine chapters of his life. Each chapter is illustrated by period photograph—the scrapbook includes about 100 photographs—and Twain's personal observations. Excerpts of about 15 letters written by Twain are included, as are some 25 news clippings of his lectures, travels, and public appearances. Visitors can also see approximately 20 drawings from first editions of some of Twain's books. The scrapbook offers about 25 audio clips of actors—most notably Hal Holbrook—reading Twain's writings and 15 video clips of the Mississippi River and other sites important to Twain's work. An accompanying chronology lists the events of Twain's life, and Classroom Activities offers five lesson ideas for introducing middle- and high-school students to Twain and his place in American history.

The site asks for sponsorship pledges and markets the video and soundtrack, but overall this site is well designed and offers valuable material for investigating Mark Twain in historical context.

Created for a 1994 exhibit, this site examines poster art as a method of persuasion during World War II. Featuring 33 posters and one audio clip--the song "Any Bonds Today?"--the materials are divided into two sections. The first, which focuses on themes of "patriotism, confidence, and a patriotic outlook," is arranged into five subsections: "Man the Guns!"; "It's a Woman's War Too!"; "United We Win"; "Use it Up, Wear it Out, Make it Do, Or Do Without"; and "Four Freedoms." The second section, also arranged into five subsections, presents posters that attempted to foster "feelings of suspicion, fear, and even hate," a distinctly different strategy of propaganda. The materials are contextualized by background essays of 100-400 words in length. Although limited with regard to number of items, the site will be valuable for those studying wartime depictions of gender and race, and the power of images to further national goals.

More than 300 U.S. government publications from World War II have been digitized for this site, an ongoing project that plans to add another 200 documents.

Materials include pamphlets and books emphasizing home front issues, such as air raids, preservation, child labor, and victory farms. All materials are searchable by title, author, subject, and keyword. Browsing is also available.

A companion collection of photographs, the "Melvin C. Shaffer Collection," depicts the home front situation in Germany, North Africa, Italy, and Southern France from 1943 to 1945. Shaffer was a U.S. Army medical photographer assigned to document the medical history of the war through major campaigns. Shafer took the photographs on this site—totaling approximately 340—unofficially with the goal of recording the war's impact on civilians.

Created by the First United States Army Group and the Twelfth Army Group, this collection consists of 416 situation maps from World War II. The maps show the daily positions of Allied army units during the campaigns in Western Europe, from the D-Day invasion on June 6, 1944, through Allied occupation in July 26, 1945. There are also more than 100 reports from the campaigns.

Maps offer insight into daily activities, but also a broad view of movement over time. In addition, they highlight the incomplete nature of information available to commanders in the field during war time. Visitors can search the collection or browse the maps and reports by title, creator, subject, place, or date. The site also includes an interactive essay on the Battle of the Bulge. Visitors can select the desired zoom level and window size for viewing maps.