Wisconsin Historical Society has many interesting links. Some that I found interesting was their research links http://www.wisconsinhistory.org/research.asp .
Here are a few free things, but you can order some good documents off their research page.
- Pre-1907 Vital Records. Search birth, death, and marriage records by last name, first name, county, and/or year http://www.wisconsinhistory.org/vitalrecords/ .
- Wisconsin Local History & Biography Articles http://www.wisconsinhistory.org/wlhba/articleSearch.asp .
- Wisconsin Historical Images http://www.wisconsinhistory.org/whi/advancedSearch.asp .
- Roster of Wisconsin Volunteers, War of the Rebellion, 1861-1865 http://www.wisconsinhistory.org/roster/ .