nvidia make the ones you mention (the choice card for me for years)
ATI are their main rivals, and i think its down to personal preference which is better..
ive got a 7900 gtx running two lcd on dvi cables and it works fine
its overkill for what i use it for now but it came into its own when playing games..
my mate spent a grand on two cards.. the SLI thing where you hook two up together.... some people have too much money!
ive never tried ATI but im sure some people here have...
but to avoid disappointment in the "if only i wish id bought the other one" syndrome, buy the best performing one you can afford and shop around as they are not the same price everywhere
i bought mine from scan (
www.scan.co.uk) but they have a shopfront in middlebrook retail park (near bolton wanderers FC)