What kind of TOEFL exam you will take? IBT? ITP? Those exams have different target and different type of tests. In my local, there are two types: IBT and ITP. The ITP is the easiest one, but it is no more recommended (since most graduate school need TOEFL IBT).

But for grammar (although it is not directly test you, but it might help), i really recommend Azar's Book on Grammar [1]. http://www.amazon.com/Understanding-Using-English-Grammar-Az...