In Unreal Tournament 3 and Gears of War for PC, there is a significant gain in having 512MB of video memory rather than 256MB. So, first and foremost, get at least a 512MB card if you can afford it. If you haven't maxed out your budget, then go for the maximum single-card performance that doesn't require extreme cooling, e.g. buy an entry-level GeForce 8800 over a GeForce 8600.