I would look into a card with 2GB of RAM. I am running ArmA 2 at 1440x900 resolution (or whatever is below 1680x1050) and I have 896MB of RAM. I used 93% of it according to Nvidia Inspector.
What setting do you use for terrain texture detail and also view distance? I would think that setting would have the biggest impact on how much video ram is used. Thanks for your info since ArmA 2 is one of my bread and butter games.
Terrain texture is set to high, and I think the view distance is set to the max or close to it. I forgot to mention this is on a GTX 260. If you download Nvidia Inspector you can see how much RAM you use. I was just suggesting to go higher than a 1GB card because if ArmA 2 is already using 93% of 896MB at a low resolution, I would not be surprised if it required more than 1GB at a higher res.
And this is why I am waiting for a 2GB 560 from EVGA (or GTX 565, 660, or some revision). At first I didn't want to go to Nvida due to driver issues, but AMD/ATI has their own issues which are just as confusing to me...