The Geography of Slavery is a digital collection of slavery information provided by the University of Virginia. The highlight of the collection is the advertisements for slaves and servants who either ran away or were captured in Virginia. In addition to the advertisements, it also includes documents such as court records, newspaper articles relating to slavery, slaveholder records and literature and narratives.
Some of the site appears to be under construction still, in particular the explanatory essays and personal profiles sections. The resources section of the site, however, does yield some nice finds. It includes a bibliography, articles explaining 18th century currency and terminology, lesson plans for teachers and links to other sites of interest.
You can browse the advertisements or if you are looking for a specific person, you can also do a full text search. You will find little information on slaveholders other than their location. On slaves, however, you may find quite a bit of information depending on the advertisement. Some include information on former and current slaveholder, description, who they are traveling with, name, assumed names and occupation. For women, it even notes if they are pregnant.
If your ancestor was a sheriff in Virginia, you may also find their name in the advertisements. Slaves were sometimes picked up and jailed until their slaveholder was located. The sheriff would place an advertisement in the hopes that the person would see it and take possession of their slave.