Photos
The source we all hope for, of course, is old photos. If your local historical society's photo collection is large, there may be a photo of your house interior in it, and if the collection is well-indexed, you may even find the photo.
Be prepared, though, to look in the files for neighboring houses and for houses of relatives of the owners of your house. It's quite possible that, when the family photo was taken in the dining room of your house in 1878, only Cousin Nelly who lived two miles away preserved a copy, and the local historian has filed the photo of your house as a photo of Cousin Nelly's house.
It's also possible that Cousin Nelly's photo album hasn't made it to the historical society at all, but is sitting in the attic of one of her descendants, who would be glad to share photos if he or she thought anyone cared about them. In researching an old house, it's almost impossible to avoid genealogy. Start with the GenWeb site for your county as a guide to what resources can help you, and where they might be located. . . and be prepared to invest a lot of time in reading decaying city directories and microfilms of the manuscript census.
Inventories
Not as vivid as a photo, but highly educational, is a house inventory, typically taken at the time of the owner's death and filed, at city or county offices, with documents related to settling the estate.
While it's more likely that an inventory was taken if the owner died intestate, don't despair (or hope too hard) until you've read the actual file. The last Johnston who owned our house died with a will, but because she had something like a dozen heirs and had not specified who would receive furniture and bric-a-brac, an inventory was done. The next owner died intestate, but since his wife was the logical heir to the whole property, there was no inventory.
