EPQ

If you are interested in the psychological side, you could do something regarding how people learn, learning disabilities or child development. I have read something pretty interesting about learning maths ( there was a study involving Amazonian tribes and Japanese chimpanzees). I would definitely say though that you really really need to be intersted Ina subject (and have plenty of time) if you want to do the EPQ (I had to drop mine as although I was really intersted in it, with 4 a levels I really didn't have the time).