Death From Above: The German FG42 Paratroop Rifle by Thomas B. Dugelby and R. Blake Stevens.
I've wanted this book for years, but the $500+ price tag of the original 1990 printing on the secondary market kept it out of my reach. Fortunately, a few years ago Collector Grade reprinted it with about 50% more content (new research, documentation, photos, etc), and I got it for Christmas a while back.
It's awesome. So much technical, historical, and anecdotal information! It's the most in-depth study of the FG-42 project I've ever seen. Makes me really wish I could afford one of the rifles, but they're about $200,000 these days, so that's out unless I hit the lottery.
If you like historical weapons, this (like all Collector Grade books I've read so far) is a must-have.