Unless the tests have changed radically in the last ten years (and nothing in the RAF changes that quickly !), the maths aptitude testing is actually set at a lower level than GCSE (or 'O' levels as I remember them !).
They do, however, put you under a great deal of pressure, timewise, and any book you can find dealing with time/speed/distance problems will aid you greatly.
The IQ Testing-style books will also help you a great deal with the pattern recognition and spatial awareness sections.
As Big Bird rightly points out though - those tests are the least of your problems. From now until your interview you will need to read a quality newspaper every day. You will need to know who is who in the governments of the world, what the trouble spots are and why, where the RAF is (and why !). Find out about your training - stand out, basically.
There are no quick fixes to this one, I'm afraid. Either you're the gung-ho, rip-the-clothes-off-and-charge-stark-naked-at-Welshmen type (just for you WWW), can command a group of spotty teenagers with aplomb across a make believe mine-field, drink like a fish with the rest of the course and still turn up at 4am perfectly sober, crack a dirty joke and then whip round and discuss the problems of financial restructuring in the former Yugoslavia... or yer not.
Maturity and life experience, I believe, are the key, and they are rare qualities in people the age the RAF need to recruit. Rambling aside, I'm sure you know what is required. And remember, if you don't succeed first time, just keep going back until they get so fed up with you they let you in.
Worked for me... three times I went to Biggin Hill to be told to come back a year later. Not mature enough they said, and looking back, they were right.
Best of luck - if you want it enough, you'll get in.