If you want the most complete library, get the manuals for every bullet manufacturer. I have Hornady, Speer, Lapua, and Sierra. Plus I have the Hodgden manual and Quickload. I believe information is king (then again I'm pretty anal and obsessive about some stuff - like reloading.
I have the Hornady 6th edition double volume which would have to be the best publication available for both Data, Reloading and ballistic how it works information.
I use alot of Hornady projectiles (just seem to be the most accurate in my rifles) however alot of the reloading data is usless here in Aust. as many of the powders are unavailable or the ones that are are expensive (I use the locally grown ADI powders, which are actually exported to the US and sold under the Hodgson label).
Also I have the ADI, Winchester, Lyman 46th edition and Serria manuals.
Also i use a variety of ballistics programs, Point Blank, Ballistics Basics elite and Serria Infinity.
Well I would like to add something to this topic but it has been said very well by the rest of you all, I guess I can say that it is ALL IN THE DETAILS, case type,primer brand,powder weight,bullet weight, even down to how you cleaned the old cases, use many different manuals find what works for your weapon and then stick to it.