Should be first on the list for anyone taking the exams:
Bristol Online Question Bank
http://213.48.96.23/atponline/jalo/index.asp
Books:
Aircraft Performance Theory for Pilots
P.J. Swatton
ISBN 0-362-05569-3
For the Technical aspect of the course:
The Commercial Pilots Study Manual
Mike Burton
Volume 1 - 4
ISBN 1-85310-779-4
ISBN 1-85310-780-8
ISBN 1-85310-781-6
ISBN 1-85310-782-4
Navigation type of the course:
Ground Studies for Pilots
R.B. Underdown
I only have Volume 1 and 2 but there are 4 in the series.
Last but not least:
Oxford Aviation / Meteorological Office "Meteorology for Pilots CBT"