Now, a lot of people have mentioned that your crosshair will be right in the middle of the two screens. In most cases, this is wrong.
99.9% of games don't support spanning across mulitple displays. It won't be 2560 x 1024, it would be 2 x 1280 x 1024 (VIC, check your math ^_^). So, you'll get the game on one screen, and your desktop on the other. For productivity, it's great, but for gaming, dual displays doesn't do much.
My suggestion would be to go with a large single monitor, preferably widescreen. The Viewsonic VX2025wm 20" (the one I'm using now) is incredible, big, bright, sharp, and clear. Blacks are decent, as LCDs go, and no detectable ghosting in UT2004, FEAR, or big PvP battlegrounds in World of Warcraft. Highly recommended.
1680 x 1050 is a great resolution, and more and more games support it natively, like WoW, Oblivion, etc. Others, like BF2, FEAR, and the like need some pretty simple widescreen hacks to get it working at native. You're going to find that widescreen is much better supported than dual displays, as sweet as they are.