THanksi do not have any recommendations. and the CGP workbooks, those come by topics, right? which one(s) do you have?
you might find the following links useful. some have books listed, you can find reviews of them to decide if you think they'll be a good fit. others are just helpful sites or advice.
EasyMaths - Free GCSE Maths tutorials, Sample Maths Exam papers, Books, Puzzles, Magic all helping to make learning maths easy!
What are the best GCSE Revision Sites/Books? - Yahoo! UK & Ireland Answers
GCSE Maths Books
maybe e^(i*pi) will have some recommendations...