if your from the uk:
www.overclockers.co.ukif your from usa
www.newegg.comp.s. with the current exchange rate it might actually be cheaper to order from an american country even if you live in the uk

pps those cards i listed above are the minimum cards i would reccommend ( a good rule of thumb is that more expensive the card is the better it is

(remember to get ATLEAST a 256mb card for fsx (mines a 128 but it doesnt have enough memory

)
ppps before you buy a card you need to know if your motherboards pci express or agp, otherwise you risk buying the wrong card and not working.
final note: post this down in the hardware forum and post a link, they should give you second opinions on the matter...its surprising that its only me and one other person posting here...a few months ago EVERYONE wouldve tried to help you...