George F Nafziger
I had a very pleasant exchange of emails recently with Rasmus, from Portugal, on the subject of Spanish OOBs, and it reminded me that I do get occasional queries from various enthusiasts wondering about where to find good, detailed information about the various armies of history. My Salamanca OOB article for the Grand Tactical Game raised a number of requests for sources, for example.
I always direct people to the George F Nafziger collection, which - incredibly - is now freely available to the public online. I say incredibly because previously these things were available only by applying to Mr Nafziger himself, and cost a few dollars a page.
Anyway, the place to look is on the website of the US Army Combined Arms Center, which sets out an enormous list of files, in pdf form, which you can read or download.
The names of the files are coded, and to make sense of them you need the index. The index itself is rather hard to follow - the Napoleonic period, for example, appears in several different places. The best way to use this index is to download the complete thing (it's another pdf) and do automated searches on it for key words (e.g. "Prussian") to find the various relevant entries. Thus, for example, the index will tell you that 808GSAH is the Spanish Army at Baylen, which you can find in the main list and open up.
This is a real treasure house. Mr Nafziger is to be heartily complimented, not only on his achievement in collating the information in the first place, but also on his magnificent generosity in donating the information for public view. To those who are familiar with this resource, and its whereabouts online, I apologise for the old news, but to anyone else I have to say that I cannot recommend this library highly enough.