Randy Seaver has posted about a talk by Ann J. Miller concerning lesser-used research resources. I've not heard that talk, but I have had some experience with some of these resources. Here I explain where and how to find some of them. Not all are online and some are not available in microform, either. So finding some of these records requires the good old fashioned hard working genealogical research.
Land and property records
These are mostly available on microfilm from the Family History Library. More recent records are available online in many jurisdictions. A good example is the Jackson County, Missouri site. These sites vary in terms of what is available and whether there is a charge. Jackson County, Missouri, provides PDF copies of documents for no charge. On the other hand, Nacogdoches County, Texas, charges a modest fee ($2.00-$3.00) for copies of documents. [its documents are handled online by a commercial concern].
These records include wills and guardianship records. The records are mostly available on microfilm from the FHL. Only a few jurisdictions have these records online. An example is Nacogdoches County, Texas. Probate records include information about many folks other than the decedent. You will learn about children, spouses, executors, appraisers, accountants, and lawyers. For example, last year, I wrote to the Milam County Clerk in Cameron, Texas, for the probate files of Reuben Henry Sanford and Martha Sanford. I learned a number of things that I did not know.
In 2005, I went to Thomaston, Georgia, to examine records of Upson County. I looked through original probate records in the chambers of the local probate judge. It was quite interesting. If you live close enough to the jurisdiction in which you are researching or if you have reason to go there, looking through the ancient books adds another lively dimension to your research adventure!
Assessment and tax records
Mostly available on microfilm from FHC. More recent records are available online in many jurisdictions. See for example, Aransas County (Tex.) Assessment District.
Court records, including divorce records
Some are available on microfilm from FHC. More recent records are available online in some jurisdictions. Examples include the Missouri circuit courts and the Los Angeles Superior Court. Online sites vary in terms of what is actually available. Note that California's legislature is considering a bill to restrict divorce records---seems to have been motivated by a rich guy's embarrassment about having his financial information available to public in a property settlement. It's not clear that this controversial bill will pass.
As Randy notes, obituaries can supply information about not just the deceased, but for parents, siblings, and children. There are several commercial site on-line such as obitsarchive.com and newspaperarchives.com. A number of public libraries have obituary indexes, usually in cooperation with a local newspaper. A good example (heck, the best example) is the Corpus Christi Public Libraries site. They will e-mail or snail-mail copies of obituaries from the Corpus Christi newspapers. Not all libraries will do that.
Passport Applications . . .
. . . have a variety of information. But note that passports were generally not required before 1941. Passport applications up to March 1925 can be found at the National Archives and Records Administration and from April 1925 to the present at the State Department. To obtain the passport files of a deceased person, you must file a request under the Freedom of Information Act (FOIA). This the same provision of law under which you obtain the Social Security applications (SS-5). The State Department has a handy "FOIA Letter Generator" that makes this process simple. I'm going to try it and will report back on how long it took, etc. You can also request the passport files of a living person with proof of their consent.
More to come on uncomon resources!