The great state of Tennessee has more lists of online archives than it has double-letters in its name. Might as well get right to it.
Tennessee State Library and Archives list of its key Digital Collections is actually a list of other lists, some of which I'll detail here:
Tennessee Virtual Archive (TeVA) -- a very nice collection marred by a clumsy interface and a deliberate effort, all too common at some archives, to impose user-unfriendly limits on image access.
Nashville City Directories -- Complete directories, beginning in 1853
Tennessee's Landmark Documents -- Significant documents in the formation and early history of the state
Photograph Database -- An index to offline content
Tennessee Government Web Archive -- Archived state government webpages.
There are a number of excellent Civil War Resources:
Historical Newspapers (19th Century) has the unusual feature of being accessible only to residents of Tennessee (or at least, those who provide a TN zip code and phone number...hint, hint)
The list of Research and Collections at the archives is too long to go into full detail here, but here are the main headings:
and here's the breakdown of the individual collections (told you there are a lot of lists!)
There's a lot of material in those collections for family history researchers, such as the Davidson County Death Records 1900-1913 and the Index to Tennessee Death Records 1908-1912.
Over on the Exhibits page, you'll find brief, informative write-ups and some interesting archived materials on a variety of topics (another list coming...):
The Photograph and Image Search tool almost makes up for some of the other user-unfriendly content at the archives. This is an easy to use image search that offers up good quality images in the results.
Lastly, the East Tennessee State University -- Archives of Appalachia is an extensive list of links to other TN archives with mostly offline content.