Essential Grammar in Use: with answers (2015) Probably the most comprehensive collection of grammar exercises for self-study. Essential Grammar in Use is suitable for beginners (CEFR A1).
English Grammar in Use Book with Answers and Interactive eBook 4th Edition Suitable for intermediate students. Lots of exercises and interactive content. Use it alongside English lessons to improve your English even further.
Advanced Grammar in Use Book with Answers and CD-ROM 3rd Edition Suitable for exam preparation (CAE, CPE IELTS etc.) Great resource for self-study alongside English lessons!
English Vocabulary in Use Pre-intermediate and Intermediate Vocabulary in context! On the left are explanations and examples, on the right are the exercises. Very useful for self-study.
Collins Concise School Dictionary (Collins Primary Dictionaries) English - English dictionary, with easy to understand explanations. Suitable for (pre-) intermediate learners, as a first monolingual dictionary.
Oxford Phrasal Verbs Dictionary: For Learners of English (Diccionario Oxford de Phrasal Verbs) Phrasal verbs dictionary. Indispensable reference book for intermediate and advanced students.
English Phrasal Verbs in Use: Book with answers Lots of exercises to teach you how to use phrasal verbs in context.