Mandatory reading
There is one book that all students should have read from cover to cover before starting the course:
Goldschlager, L. & Lister, A. (1988). Computer Science - a
Modern Introduction. Prentice-Hall (2nd ed.).
You should also try some of the exercises. In particular, the first 15 exercises at the end of Chapter 2 on the design of algorithms and the first 10 exercises at the end of Chapter 4 on computer architecture are relevant preparation for the introductory lecture courses.
Many students have some difficulty with the mathematical aspects of
the first-year course. A little study of pure mathematics would be
valuable. It will also help to pursue recreational mathematics in the
form of games and puzzles to keep your skills tuned.
General reading
After the technical reading suggested above, the next most important preparation is to build up a broad background understanding of current issues in Computer Science. An excellent informal collection of accessible and relevant articles can be found in:
Dewdney, A.K. (1993). The New Turing Omnibus. Computer Science Press.
Byte and magazines like New Scientist and Scientific American often have relevant articles; popular computing magazines tend to have a commercial emphasis which is less useful. The April 1995 issue of Scientific American had a set of particularly interesting articles on The Computer in the 21st Century.
Course reading
You might like to look at some of the text books that are listed elsewhere in this document. Printed notes will be handed out for most courses, so you don't actually need to buy all of the books.