I would like to know your recommendations when it comes to an English dictionary, slang guide and the like. Of course, I already have an English-English dictionary, but it's not what it used to be -- my expectations are probably too high. By the way, I'm focused on American English. There are so many books out there, choosing only four or five good ones is pretty hard. Any suggestions? Mine can be seen below.
Swan, Practical English Usage Garner, Modern American Usage Green, Cassell's Dictionary of Slang, 2nd edition
In terms of grammars, I still find Otto Jespersen, A Modern English Grammar (out of print) the best, especially in terms of examples from the literature. Get at least vol. IV (dealing with the verb) -- copy it at a university library.
My two books which I keep returning to is, a) The Oxford Essential Guide to Writing, and b) The Oxford Advanced Learners Dictionary, 8th Edition.
The Oxford Essential Guide to Writing, is a great book, but it needs getting used to. The language is elaborate, but the advice is very effective. I believe, this is the book of choice in the United States.