Some links to great stuff on the passing game, courtesy of Amazon. As of this writing, all of these are currently available with free Super Saver Shipping.
The Bunch Attack: Using Compressed Formations in the Passing Game by Andrew Coverdale and Dan Robinson. This has become an offensive classic. More than just describing bunch formations, it's sort of a crash course in how to use an offensive system to really attack a defense. Basically, Coverdale and Robinson had written the best books on the passing game for many, many years.
Football's Quick Passing Game:was a great series by the same authors of "The Bunch Attack" that largely expanded upon the principles and basics laid out in the earlier book. The Quick Passing Game trilogy has rightfully been praised. Unfortunately, Amazon is only showing Vol. 3 as being in stock at the moment.
Concept Passing: Teaching the Modern Passing Game has, in my opinion, actually surpassed the great Coverdale and Robinson books that were the standard for years. Gonzalez, who has coached at the University of Texas as well as at several other high schools and colleges, really boils down the passing game to a simple level. In one concise volume, Gonzalez really demystifies and explains the passing game in ways that are useful and effective to any coach. This is a must-read.
The Complete Handbook of Coaching Wide Receivers: The Difference is in the Details by S. "Chuck" Meyers. If you or someone you know thinks that all there is to coaching wide receivers is yelling "catch the ball!" at them with increasing frustration, there is hope. No part of WR play goes uncovered, and unlike in some coaching books I've read, she provides great pictures that demonstrate her coaching points throughout. This is basically the best book (Slack's DVDs are still the best *resource*) on coaching a position that I've ever read.