I've just finished Noam Chomsky's "On Anarchism" which has a lot of historical information about Catalunya's collectives, anarchism and syndicalism. I've heard Gabriel Jackson's "The Spanish Republic and the Civil War, 1931-39" is a good account but Chomsky and George Orwell in his "Homage to Catalonia" disagree with a lot of the points Jackson makes or the points he brushes over as not that important. Having not read Jackson, I can't compare, but I would like to read the best and accurate account of the Civil War. (In English)
Orwell is incredibly engaging, but Homage is a primary source account of the war from a single participant who was invested in one particular view of a war that was a veritable alphabet soup of factions. As for Chomsky, he wears his views on his sleeve, so I don't think I really need to point out that he has a very specific lens he views the war through, that can be at odds with other sources. I don't think I'm being hyperbolic to say the SCW is one of the most politicized events of the 20th century, and where you stand definitely influences how you see it. As luck would have it, I've been working on revamping my Profile Page, and while it is still a work in progress, the Suggested Reading section for the Spanish Civil War is looking pretty now As I note there, "The Spanish Civil War" by Hugh Thomas is what you are looking for if you want thorough and comprehensive. It is well respected, and although published in 1961, comes in a revised edition updated in 2001. As long as 1000+ pages doesn't scare you off, that's what you want to go with.