That's a good combination of subjects - given that you've got maths and further maths (not essential, but a great help).

Psychology is fine, as for other subjects, I'd advise choosing your 4th subject on the basis of what you enjoy doing.

Politics and Geography are not generally considered to be light subjects (though at the same time, not everyone regards them as highly as say, Maths) - they don't appear on either of the 'subject blacklists' produced by LSE and Cambridge (whereas Business Studies, as you suggest, does).

E-mailing admissions tutors would be a good start and I'd also think about the subject matter and which of the two you'd enjoy more as both are linked to/support economics.

Having done Geography, I can say it's a really enjoyable subject (field trips and other excuses to leave school and do some 'work' near rivers and stuff is always welcomed). It's got a big overlap with development and you'll study similar issues in Economics but from a slightly different angle. A lot of Human Geography is relevant to other areas of Economics too, and it's always useful to know what different parts of the world are like culturally/socially and economically, something I placed great importance on.

Politics on the other hand was a subject I considered doing but then decided against so I'm not as clued up as to the specifics of what it involves but you'll most probably be looking at forms of organisation (of government rather than firms) which is something management also looks at. Friends of mine who took Politics were more aware of historical economic circumstances (e.g. that a lot of privatisation took place under Thatcher in the 80s and trade union power was reduced) but you should be able to pick this up even without taking Politics anyway!

My advice - if you're picking this as a 3rd A-Level, I'd definitely email tutors and see what they have to say but if it's a 4th subject, pick the one you think you'd enjoy most as they both have their pros and cons - good luck!