Richard Byrne, author of Free Technology For Teachers, recently posted links to several U.S. History Resources.
Teaching The Civil War With Technology is a comprehensive website that provides teachers with lesson plans, tools, tips, and strategies for teaching the American Civil War. A podcast is also offered and would be a great resource for students as well.
The HipHughes History YouTube Channel is another great resource for both teachers and students. Keith Hughes is a U.S. History and AP Government teacher who covers important historical events by breaking them down into short, educational, and entertaining YouTube videos.
History Tech is a blog written and maintained by curriculum specialist Glenn Wiebe. Glenn covers tech, history, and current events in his posts and also offers lesson plans as well as an interesting podcast series covering U.S. History topics.
The National Archives offers an entire website of U.S. History resources with links to already prepared lesson plans and documents. Through DocsTeach, the National Archives also offers customizable, interactive activities built around primary sources.
The Library of Congress offers a "Today in History" feature on their website. Every day a different historical event is posted about in this feed along with artifacts or images associated with that event.
Each of these sites has some great stuff!