There are a number of quality research-oriented websites available that may assist in locating information about United States history. In addition to the general history web sites listed under the web sites tab, the following may be of interest.
Use these resources to find out about primary sources, what they are, and where to find them.
E-books:
Bartleby's - A selection of ebooks that includes primary source material. In particular, check out the titles "World's Famous Orations," and "Harvard Classics," for some great examples.
Web-based information: