Your monitor's max resolution should be 1920x1200.
Couple of things- depending on the games you are playing, 1 relatively high powered graphics card should be enough. Something in the $150-250 range. However, if you are playing some of the most graphically intensive games with all settings turned up, you may start to reach the limits of what that caliber of card can do. Identifying your resolution and the types of games that you play is a good way to start narrowing down what level of performance you need (and therefore what kind of graphics setup will suit those needs).