(this is for the old specification of Psychology, just to be clear for the edexcel examination of psychology that has currently past papers ranging from January 2009 to June 2015)
My predictions for unit's 1 big (12 marks) question are:
a) Milgram's agency theory, i think it's a possibility yet not one of the most likely as in 2014 there was a study of obedience so they might avoid choosing obedience again.
b) Theory of memory, a key subject of the material, it has been 4 years from the last paper it was chosen, it's another possible choice.
c) Social Identity Theory, it was only entered once as this big Q in 2011 with a case study given, but i think case study or not it's going to be this year's big question.
d) Comparing of methodology, Qualitative VS Quantitative, Lab experiments VS Natural experiments etc. GOD I HOPE NOT but it's unfortunately another very possible choice.
I would rank these according to possibility with: Social Identity Theory 45%, Comparing Methodology 25%, Milgram's Agency theory 20%, Theory of memory 10%. DO NOT TAKE THESE FOR GRANTED THESE ARE PREDICTIONS.