South Dakota Office of Tribal Government Relations http://www.state.sd.us/oia/oia.html#Tribal
Official site, with information links to nine tribal offices.
This page is a listing of all the treaties and information
on them made between the U.S. government and Sioux tribes.
You can view some of the original treaty texts.
South Dakota Government and History
This is a huge lesson on tribal government and citizenship,
and is probably beneficial to all ages, though it is written
for 4th Graders. The main page is at http://www.sd4history.com/