Milestone Documents in American History is a robust online database that includes the complete content of printed reference sets, free. Purchasing printed reference delivers online access at no additional cost. Salem currently offers this service with three series of historical reference: Milestone Documents - A new, primary source series; The Decades - Salem's critically acclaimed American history series; Great Lives from History - The definitive, worldwide biographical resource.
Links
[1] http://www.history.salempress.com/