I've just finished my GCSEs, but this is what I took:
Triple Science - I've always really enjoyed science and it was reccomended if you wanted to take it further. Though, they did say that it wasn't compulsory if you wanted to do it for A level.
French - Our school encouraged us to aim towards the English Baccalaureate, so my mum was really keen that I took it. I would have taken it anyway though, I really like languages, though the aural exams were terrifying and so stressful! I also wanted a language as they can increase your employment chances.
Graphics - Back in year 9, I was really interested in Graphic Design and so thought it would be a good idea. It was kind of rewarding at the end, but I had no life at all during this summer. I was going in every lunch time for over 3 months to try and get my controlled assessment done. So unless you're willing to put the hours in, I wouldn't reccomend it.
Geography - I found it easy and before the GCSE course, I also really enjoyed it. However, the course my school followed was really dull. If you are good at it, take it, I found that having a subject I was confident in during the exam season helped take the pressure off.
Art - I just adore the subject. Though I was no where near prepared for the amount of work you have to do.
LikeEmyJ14, I was also in top set for maths but I took my GCSE early. From November 2012 I was learning the first module of the A level, though that wasn't really an option.. Everyone in my set did that.