You don't mention what level you're at ie PPL or ATPL but I would recommend the Oxford Met CD (ATPL). I did the ATPL's on the strength of it and I got 89% (14% wasted effort, only kidding) Of all the futile exams, Met, I believe, is probably the most relevant and will stay with you all your flying career. I have absolutely no attachment to Oxford, but the CD does tend to tick the boxes and is easy to follow. Use it as a back up to your knowledge of the subject and it should re-inforce your previous knowledge
Good luck and remember, the weather is totally unforgiving, having a sound understanding of it will probably one day save your life
