Where might one find an inexpensive MacBook Pro?

I fear my current laptop is coming to the end of its cycle as my primary machine and i now require something a little more powerful. I would like a 15” Macbook Pro that i can use to power through all my Photoshopping and movie editing needs, so i would like a machine with a fairly capable graphics card and a decent processor. Memory is fairly easy to upgrade so this is not a major concern.

Is there any place where i might be able to purchase a good quality second hand or refurbished Macbook that won’t break after a week? I did consider the apple refurbs but even they are only £100 or so cheaper than the normal prices and i can get 14% discount as a student there so not being able to purchase the refurbs instore means its cheaper to buy new from Apple.