The Library of Congress has an enormous collection of primary sources on a range of topics, most related to United States history, but they have some global collections too. Consider browsing their digital collections to see if you can find a topic that interests you.
Here are a few to whet your appetite:
The Digital Public Library of America gives you access to over 29 million images, texts, videos and sounds across the United States. You can browse by topic, check out online exhibitions, or check out their primary source sets. Here are a few of their collections that might interest you:
University of California San Diego has a great guide full of links to digital archives and other primary sources on a range of topics. Here a few of the many resources listed:
American Historical Documents - The 47 treaties, speeches, historical accounts and governmental documents in this collection trace the United States from the settling of the continent to the founding of the country to the Civil War and early twentieth-century international relations.
Hurricane Digital Memory Box - Digital objects including images, podcasts, videos and blog postings of personal accounts from those affected by Hurricanes Katrina and Rita.
The September 11 Digital Archive - uses electronic media to collect, preserve, and present the history of September 11, 2001 and its aftermath
African Posters - A collection of posters created by African governments and international agencies, as well as political/labor/social/religious/educational/ cultural organizations. Topics include anti-apartheid movements; HIV/AIDS; Lusophone African liberation movement; Nigerian social values; 1994 South African elections; and South Africa under apartheid.