Books about teaching in virtual worlds:

Molka-Danielsen J. & Deutschmann, M. (Eds.), Learning and teaching in the virtual world of Second Life. Norway:Tapir.

Learning in 3D by Karl Kapp and Tony O'Driscoll.

Transforming Virtual World Learning (Cutting-Edge Technologies in Higher Education), edited by Randy Hinrichs of 2b3d and Charles Wankel, is a self proclaimed practical guide with case studies from around the world.

Expected 2012, the "Ethnography and Virtual Worlds: a Handbook of Method" Tom Boellstorff, Bonnie Nardi, TL Taylor, and Celia Pearce; Princeton University Press.

Libraries in Virtual Worlds

Virtual Worlds, Real Libraries: Librarians and Educators in Second Life and Other Multi-User Virtual Environments by Lori Bell and Rhonda B. Trueman.

Books about making stuff for virtual worlds:

Online free wikibook Blender 3D: Noob to Pro