If the problem is really that you have such an overabundance of possible topics that you can't possibly choose, then I think it would be helpful for you to list some of them -- along with a sentence or two describing what you'd argue or explore concerning each one. Then people here might be able to tell you what sounds most interesting or potentially fruitful. We don't know your background (psychology is a big field, to put it mildly) or interests -- without some indication of those, this has more the feel of a fishing expedition.
I'm picking a topic for my Psychology Honours dissertation next year and I've got so many options and interests that the overabundance of choice is near paralyzing. So in the interests of crowd sourcing and hopefully writing about something of substance, I'd like to hear suggestions for potential directions I could take. It can be any idea but one that frequently pops up on less wrong and needs further exploration or exposure would be ideal.
Basically feel free to offer suggestions but ideally I want something that (assuming I do it right) would help lay a part of the groundwork required to build up someones rationality.