A Reference Grammar of Modern Standard Arabic (Reference Grammars)

This book spells it all out for you and covers what you need to know and what the nerds want to know. It's easy to read and clear and i've lent it out to many of my friends who studied/study Arabic and I recommend it as an essential if you care to take your studies of Arabic past the second year. I'm soon going on to graduate studies in Arabic and still always have it handy. Once you have your grammar down, learning Arabic becomes an entirely different process and being able to use your knowledge of grammar just makes the seemingly infinite number of words and morphological variations present in Arabic not so daunting because you're able to dissect every word and you pretty much only need your Hans-Wehr. And when a dictionary is the only thing you need left when studying a language, you're pretty well off.