You started your post by saying ". . . I want to have 2G memory". We try not to immediately argue with someone who is already convinced of a want or need. So it took a while for folks to tell you 2G isn't necessary; in fact, since that memory needs addresses, it can restrict your system's use of main memory.
As for which video card . . . frankly, I try to satisfy my own video requirements with a single video card because (a) MMOs haven't responded well to SLI/Crossfire, and (b) neither do some FPS games. So I would look to 4870, maybe even 4890 . . . or 260-216, 275 . . . and run with it, adding a second later if I needed it and if no new cards had been released by then.