I don't know if you already have the information you need (since the original post is from 2011), but I still figured I would give it my input. It might help someone, if you are already covered. *smiles*
Book examples:Sumer and the SumeriansBy Harriet CrawfordA book written for students about Sumer.
Myths from Mesopotamia: Creation, The Flood, Gilgamesh, and Others
By Stephanie DalleyThe title says it all, Myths of Mesopotamia. Based more on Akkadian sources rather than Sumerian.
The Literature of Ancient SumerThe late Jeremy Black, Graham Cunningham, Eleanor Robson, Gábor ZólyomiA book about Sumerian literature. Expensive as hell, I'm still saving to buy this one.
I've found that when you are using a book written about Sumerian religion as a source, you have to make sure that writer actually knows what they are talking about. There are surprisingly many books written by people, who have very little or no knowledge at all about the society and culture of Sumer. They just take myths and their own assumptions of what it was like back then and make their interpretations based on that. So, I prefer to use books that have a lot of information and historical facts (or are accurate translations of historical texts). But it's just my personal preference.
Other source examples:http://etcsl.orinst.ox.ac.uk/edition2/etcslbycat.phpThat's a site hosting translated Sumerian text's that some feature the most important Gods and Goddesses of their religion. The text are quite fragmented, but it still is a good free source.
http://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=1116&context=stu_hon_thesesA Journey Into the Land of No Return: Death Attitudes and Perceptions of Death and Afterlife in Ancient Near Eastern LiteratureBy Leah Whitehead CraigThesis. I find that source lists in academic works are quite useful. And of course, I usually read the actual papers too.
http://www.sumerian.org/sumerlex.htmSumerian Lexicon. A language resource. There's also a print book by the same author (
Sumerian Lexicon: A Dictionary Guide to the Ancient Sumerian Language by John A. Halloran), which in my opinion is easier and more comfortable to use than the online source. But if you don't want to pay around 50 pounds, then I'd say go with the free source.