The Burial Grounds were rediscovered during excavation in preparation for building another high rise, which caused an immediate halt in favor of archeological research on the remains conducted at Howard University. The links here provide extensive history of the burial ground as well as its recent development since its rediscovery in the 1990s. Although much of lower Manhattan was built over the burial grounds (including City Hall), there has been a memorial to the slaves erected with works by a number of artists, including the black woman sculptor Barbara Chase Riboud. Her work is a tribute to the entire African Diaspora and provides a fascinating commentary on the blues consciousness of 20th century African Americans.
This is a site that can be easily visited if you live in New York. Also, the work on the African burial grounds provides a link to the extensive work online from the exhibition of slavery in New York put together by the New York Historical Society, accompanied by a collection of essays on the topic edited by Leslie Harris, included here on my Slavery wish list at Amazon.com.