This page was specifically designed for graduate students in U.S. history and American Studies. Also be sure to see the American Historical Association's online guide Graduate School From Start to Finish.
Number One: Worldcat
This essential database is a catalog of library holdings around the world. Because it notes whether Yale owns items, Worldcat can work as a substitute for Orbis. Worldcat is also a great way to find both secondary and primary sources, as it is easy to limit results to items held in archives. It is also easy to discern where items are held, in which case you know whether you can use Borrow Direct, ILL, or a research trip to get access to them. There is a free version of Worldcat, but it is much less comprehensive than the subscription version.
Number Two: ArchiveGrid
ArchiveGrid is a collection of nearly two million archival material descriptions. Archival collections held by thousands of libraries, museums, historical societies, and archives, mostly in the United States, are represented in ArchiveGrid.
Number Three: America History and Life
Not as user-frienldy as JSTOR, but in terms of U.S. history this index is far more comprehensive. America: History and Life not only indexes more journals than JSTOR, it also includes dissertations and monographs.
Number Four: Blackwell Reference Online
This database contains nearly all of the volumes in Blackwell's excellent Companion to . . . series. To give you an idea of the quality of essays in this database, consider this Matthew Frye Jacobson essay on ethnicity from A Companion to Post-1945 America (edited by Jean-Christophe Agnew). Blackwell publishes companion books on nearly every period and subfield of U.S. history.
Number Five: Historical Statistics of the United States
Looking for reliable data on the economy, population, crime, immigration and other important issues? Consult this authoritative source of government statistics. Most sections are also accompanied by helpful essays on extant sources and methodologies of compilation.
Number Six: Proquest Dissertation Database
This database makes nearly every dissertation ever filed in the United States available in a PDF. Note that you can search by school, department, and adviser.
Honorable mention: New York Review of Books Archives
The Yale Univeristy Library subscribes to the full-run of the New York Review of Books. This is a useful - and I suspect often overlooked - resource for graduate students. Although not a peer-reviewed journal, the NYRB contains many reviews written by leading scholars. For example, here is Eric Foner reviewing Morton Horwitz's The Transformation of American Law, Edmund Morgan reviewing Gordon Wood's The Radicalism of the American Revolution, and Daniel Walker Howe discussing the historiography of Jacksonian America.
Here are four of the major microfilm catalogs that librarians and curators use to purchase collections for the Yale University Library. The Yale University Library already holds many of the items in these catalogs, but if you find something here that Yale does not own, then you can try to get it through Interlibrary Loan or ask me to purchase it. Please note, purchasing items is only useful for long-term projects. This is because it often takes over a month for a purchased collection to arrive and be ready for use, so it is often not workable for semester-long projects.
A good overview of the types of tools to find primary source material, both at Yale and beyond, is found on this Primary Sources at Yale website. All of the sources listed have their relative strengths and weaknesses. Here are my favorites:
Orbis is one of the best tools for finding primary sources at Yale. Use the "more limits" feature to find primary sources.
Worldcat is the most complete source for finding collections around the world.
Archive Grid is also a great tool for finding collections, both at Yale and beyond, though it's not as complete as Worldcat.
Keep in mind that a very good - and often overlooked - source of primary source material at Yale can be found in the Microfilm Reading Room in the basement of Sterling Memorial Library. This link brings you to a list of major microfilm collections available in the Microfilm Reading Room.