I like Macmillan readers for studying. They are simplified and you can choose your level.

I love reading.  Which books you would enjoy and find helpful would depend on what you like to read.  There is also a big difference in English witting styles.  The novel I'm currently reading is written in the style of historic deep southern America (author Harper Lee).  I can imagine it could create a lot of frustration for anyone trying to read it with English as their second language.  I find myself (a native speaker but from the northern mid-west) re-reading many paragraphs as the references are obscure and the chronology is complicated. British English has it's own style and variations as well.  Do you have a favorite type of character or subject?  

Which is your level? There is a book that I like too much called "Touching the Void" by Joe Simpson.

If you are an Intermediate Level is a cool book.