I really like the books in the Jossey-Bass series on Online Teaching and Learning . There are two books coming out this fall/winter -- Using Wikis for Online Collaboration: The Power of the Read-Write Web by James A. West and Margaret L. West, and Assessing the Online Learner: Resources and Strategies for Faculty by Rena M. Palloff and Keith Pratt. Both sound good to me and you can download a sample chapter from each at the website .
Tools and tips related to online and distance learning and using technology in instruction