RavenDB in Action: MEAP edition
This is probably the RavenDB book that I am most looking forward to. Written by Itamar Syn-Hershko, who worked for Hibernating Rhinos and is mainly responsible for the fact that I understand how lucene works.
You can get it here: http://www.manning.com/synhershko/
Use coupon code ravdbco to get 50% off the original price