Here is a slave trade data base that uses thousands of documents to show much of that trade.
Developed by historians Historian David Eltis and David Richardson, the data base includes information on almost 36,000 voyages.
You can search the data base for particular voyages, examine estimates of the trade, or even explore African names.
I explored estimates of the slave trade. A table shows the number of slave voyages by country between 1501 and 1825.
You'll see that Spain sponsored far more voyages than any other country. A timeline shows the the number of voyages by year and maps show the source of embarkation and disembarkation. The map is interactive and you can click specific areas and a menu pops up showing the sources and number of slaves disembarking at specific location in the America.
The site work work for an interesting webquest.