I thought it might be a good idea to have a non-fiction thread, to complement the other threads for Read an E-book Week.
Soldier / Geek: An Army Science Advisor's Journal of the War in Afghanistan by Glenn Dean (REW50 for 50% off). I've bought this, but not read it.
In Search of Lethality: Green Ammo and the M855A1 Enhanced Performance Round by Glenn Dean is free. I found it to be an accessible book about a technical subject.
An Introduction to Hadrian's Wall: One Hundred Questions About the Roman Wall Answered by M. C. Bishop (REW50 for 50% off)