The Emory University Libraries have published Strategies for Sustaining Digital Libraries. A PDF version of the book is freely available, and a print version is available from Amazon for $15. The book is under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License.
Here's an excerpt from the book's home page:
The articles of this monograph provide resources for digital library stakeholders who seek to better understand how to effectively evolve such efforts from short-term projects to long-term sustainable programs. The monograph includes contributions from leaders in major digital libraries that have made such transitions or which are systematically considering the question of programmatic sustainability, including representatives from the National Digital Infrastructure and Information Preservation Program (NDIIPP) and the National Science Digital Library (NSDL).