http://www.archives.gov/ is the website for the National Archives. The National Archives are the official record keepers of the United States. This website is a good starting point for doing overall research, and for more information on land patents.
This bulletin published by the National Register of Historic Places gives advice on researching a historic building. It is written as though the property is being researched for nomination to the National Register, but there is still useful information found even if that is not the end goal.
http://www.cyndislist.com/ is a website used primarily as a starting point for genealogical research. There is also a section on the website for the research of house and business histories. This should be most useful when just begining the history of the home or for researching the genealogy of previous occupants.
http://www.nps.gov/tps/how-to-preserve/briefs.htm gives links to all of the National Park Service's Historic Preservation Briefs. These briefs are primarily used to give information on appropriate ways to preserve and rehabilitate historic properties. However, most give a brief history of the item in which they are discussing. This may be useful in the research of a property's history.
http://www.zillow.com/ is a real estate based website that gives basic information on a property such as its estimated value, approximate size, anemities, walk score, and the closest schools. It is useful for obtaining a quick, contemporary picture of the property.