Let's Go2

This book is ideal for elementary children especially first graders. It introduces basic grammatical patterns as well as vocabulary. It comes in six levels.

http://englishtips.org/1150794096-lets_go_book1_fixed_cd2_audio.html

This book is meant not only for teachers, but also for students of English language. It consists of interesting material for conversations, lists of vocabulary that are under each of the 30 interesting topics. There are also funny pictures.
The fundamental aim of this book is to encourage your students to speak more and also to improve their vocabulary.

Cleaned, cropped version added Thanks to lanagreg

A Cure For The Common Word: Remedy Your Tired Vocabulary with 3,000 + Vibrant Alternatives to the Most Overused Words

Make your ailing vocabulary go from merely good to exceptionally splendid and stupendous!

http://englishtips.org/1150815036-a-cure-for-the-common-word-remedy-your-ailing.html

Academic Vocabulary in Use

The perfect study aid for anyone using English for their academic work. Academic Vocabulary in Use is the perfect study aid for anyone using English for their academic work.

English Vocabulary in Use (Upper Intermediate & Advanced)

English Vocabulary in Use Upper-intermediate is aimed specifically at upper-intermediate level learners. The material has been thoroughly revised following feedback from users of the first edition.