The New York Public Library has a terrific online exhibit about Africa in the Indian Ocean from the 7th century through the early modern period.
The exhibit includes short essays, images, video clips, and maps.
Click on essays, then East Africa, and you can read about the Swahili and the trading networks in which they were involved.
You can also read about the influence of the Arabian Peninsula, especiallly Yemen and Oman, on the Swahili coast.
The exhibit covers the other major players inthe Western Indian Ocean network including India, Sri Lanka, and the Maldives.
Some of the maps show African migration across the Indian Ocean.
It's absolutely worth exploring and might make for a great webquest