Principles, Algorithm & Application by Proakis and Manolakis - It is one of the most general books on Digital signal processing. Books written by Manolakis is always a standard so if you are really planning to study some good study material then download the book or purchase the book.
What I believe is that if you want to just pass the exam then it's best for you not to download the book as it looks like a novel, means to me.. If you are good in studies then it's your call. If you are preparing for any exams like GATE then it's one of the best.
SIZE - 45 MB