The price difference between the 256 and 512 is what, around 50 bucks? Personally if you plan on getting a bigger monitor in the future, you would be better served by getting the 512.
Thanks for your replies. So essentially 256MB is sufficient for my target resolution of 1440x900, but for higher resolutions, and maybe for future games, 512MB can make a difference. I can afford the larger memory, and I want this card to last me a good couple of years, so 512MB is the way to go.
However the fan on the Asus card looks cheap. Should I get another brand? Maybe EVGA?