Robust sources in a variety of media
This is a great repository of resources for studying American History and a moderate resource for world history. What is especially notable is that its repository includes a variety of media - written text, video, high resolution images, audio recordings, etc. They also link to connected material. They regularly highlight collections in relationship to pertinent events in US History, e.g. D-Day, Black History Month, Anniversary of the Stonewall Riots, etc.
How I Use It
I use this resource in a variety of ways. Sometimes, it is simply a place for me to grab primary sources for in class reading. For example, I printed up both a high resolution image of the Declaration of Independence as well as a text of the document. I then had students to try "translate" the Declaration (without telling them what it is) before introducing them the text. They learned the challenges of "translating" texts even when they're in English! When students peform research, this is a source they use for documents, images, video, and more. For example, students put together a documentary in my class, this is a place where they can access license-free content for use (such as speeches from the Civil Rights era, pictures of suffragettes, etc).