Great list of books and great advice, Dobry. Thank you very much.
I think, that when ESL learners ask for help in studying "perfect English" they just mean the want to talk as grammatically correct as possible, and they want their English to be colourful, descriptive and with good turn of phrase.
I believe the books you mentioned will help.

I still can't choose what version of English should I learn - BE or AE. What do you think? Traditional answer is "learn the version of the country you're going to live in/to visit etc." But I'm not going anywhere, so... That advice doesn't help.

How go you think is it possible for average ESL learner (not a genius) to learn AE and BE equally good and just switch between them when needed?
I know main differencies in spelling between these two, some differencies in grammar and quite a lot pairs of words that mean the same in UK and USA (like elevator/lift, underwear/pants etc.) because at school we studied British English and watching movies I spoiled it with american slang a bit. So now my English is a horrible mess.
Should I try to "separate" BE and AE or just to "forget" one of them?