The UFO Evidence, Vols. I and II by Dick Hall is a must-read for anyone even remotely interested in the subject.
Most anything by J. Allen Hynek and Jacques Vallee.
The UFO Encyclopedia, by Jerry Clark.
Those are all good places to start.
Of course, Moseley's book is probably the best if you're more interested in the UFO subculture.
Finally, I would recommend UFO Updates, which for a decade has been the premier UFO discussion board for most of ufology's big names. www.virtuallystrange.net/
and follow the link.