Vocabulary Books

ENGLISH VOCABULARY IN USE (Cambridge)

English vocabulary in use (elemantary)
http://faculty.ksu.edu.sa/27261/English%20Learning%20Software/Cambridge%20University%20Press%20-%20English%20Vocabulary%20in%20Use%20(Elementary).pdf
English vocabulary in use (Preintermediate and intermediate)
http://www.maltassist.org/English_Vocabulary_in_Use_Pre_Intermediate.pdf
English vocabulary in use (Advanced)
http://tratu.coviet.vn/download/114/English%20Vocabulary%20in%20Use%20Advanced%20with%20Answers.pdf.html

Dictionary of common errors (Longman)
http://www.fisiologia.ufc.br/ABS/Longman%20Dictionary%20Of%20Common%20Errors.pdf

English collocations in use
http://profjoseandre.files.wordpress.com/2011/08/eng-coll-in-use-intermediate.pdf