I think the Collector Grade Publications Black Rifle series is an obvious recommendation, but I'll mention it anyway. The first volume, while an essential piece of writing, is really focused more upon the pre-A2 era (just as you would expect, given it's 1992 publication date). As such, you won't find a great deal of late-derivative (i.e. M4) data within it's pages.
Black Rifle II, on the other hand, pays a quick homage to the early days, and then launches into virtually every model, variant, and accessory that figures so prominently into the rifle's history since the mid-90s. All in all, it's very well-illustrated and an excellent read. I have found an occasional error here and there (i.e. the specification chart suggests the AR6721 has a 1/7 twist, vice the 1/9 it actually has), and the author's understanding of the subject matter is more academic than operational, but these limitations are quite minor and easily overlooked.
The main obstacle you're facing here is one of price/availability. Black Rifle isn't easy to find any longer, and when you do find it, you shouldn't be surprised to pay $100 or more. Black Rifle II can be similarly elusive, but $60 to $80 will usually net you a copy if you look hard enough.
For tactical information, I also recommend Tiger McKee's published training notebook The Book of Two Guns. This rather straightforward and unsophisticated little primer reveals AR employment techniques that aren't typically shared outside of the military and the premier shooting schools. It's a must-read if you're serious about learning how to employ your shooting steel when the chips are down and the adrenaline is high.
Chief