Kadahaf, do you need 256 MB for a special reason? e.g. are you running modelling software that requires you to have that much "independent" information to manupulate on the graphics memory?
Otherwise, if you are just a gamer, as Dj-Chris said, a 6600 GT with 128mb vid ram is more than enough - and will positively violate any card that has less processing power but with 256 mb.