Here is an interesting project underway – Fordham University (in NY) has begun a project to locate and document burials grounds of enslaved Americans in the US. The project is named Vanishing History.
The University is reaching out to anyone who knows of burial grounds of slaves. Their website has a submission form and access to the project is free. A listing of burials grounds already known starts here.
I believe this will be a very interesting and insightful project to watch grow.