linguabooster.com – designed for easy reading of foreign literature in its original form. I use it for checking different forms of verbs.
preply.com – online English tutors & teachers for private lessons.
perfect-english-grammar.com – a bunch of useful English grammar exercises.
agendaweb.org – English exercises for all levels.
Cambridge English Grammar in Use – the world’s best selling grammar series. Book for self study.
Received pronouciation (RP) – also known as BBC Pronunciation is the accent traditionally regarded as standard for British English.