If you're yet to apply you want something to mention on your PS to support your application. There's not that much point simply ploughing through a textbook as you'll never remember a thing from it (and textbooks are never intended to be simply read cover to cover for that reason). So you want interesting and readable books like these: http://www.eng.cam.ac.uk/teaching/teachoff/pre-residence_reading.html
If you already have a university place and are starting in September, then go on to your university department's website where somewhere you should find a syllabus and book list for your course.