I recently ordered a copy of La Ultima Cruzada by Bob Cordery of Wargaming Miscellany fame.
Amongst his many talents Bob is a bit of an expert on the Spanish Civil War and this is a revised 2nd edition of an excellent source book with a wealth of information for historians and wargamers alike.
The book weighs in at 276 pages with chapters including a very clear chronology of the war and info on key political parties and leaders (not an easy thing to do for the SCW) and detailed information on the armies, navies and airforces for each side. There are also some guides on uniforms which include some photographs of painted 54mm figures from Bob's collection. Sadly these are in black and white so are less useful but the amount of info and the level of detail in the book is excellent.
If you have an interest in this period I'd say it's an essential buy!!