BDTNS: The Data Base of Neo-Sumerian Texts. (BDTNS is the way the words would be said in the "backwards" Sumerian way of writing things (Base-Data Texts-Neo-Sumerian)). The BDTNS provides access to tablets in museums all around the world. Like the CDLI above, parts of the BDTNS are restricted to members only, but most of it is readily available to the general public.
Sumerian.org: A wealth of information about Sumerian writing and culture, with many links to other related websites.
allmesopotamia: As the name implies, this is a website devoted to all of Mesopotamian history and culture (Sumerian, Akkadian, Babylonian, and Assyrian).