Lakota and Dakota Language Resources: Most comprehensive list of Lakota language-related resources and materials.
Lakota Language Consortium: A nonprofit organization working to revitalize the Lakota language. Site provides current Lakota language usage statistics as well as curriculum materials for elementary school age learners.
Siouan Language Family Linguistic Listserv Archive: The best academic resource for Siouan language related issues, including news related to Proto-languages, borrowings, and other descriptive topics.
Siouan Texts: This site has the largest collection of Lakota language texts on the internet. Great work by a committed linguist.
Sketch of Lakhota: Linguistic description of Lakhota, a Siouan Language by David S. Rood and Allan R. Taylor. Online version of article originally in the "Handbook of North American Indians, Vol.17 (Languages)", Smithsonian Institution, p.440-482, 1996.
Yahoo! Groups : lakhotaiyapi: This discussion group is helpful for learning to read and write Lakota. The site has a good number of knowledgeable members who can assist with specific questions.