I'm a fan of the dual-monitor setup. I started out with a 17" on my Riva TNT AGP card and an *old* 14" on an old Stealth 2mb PCI card when I put my system together. Nice cheap way to get more desktop space. I just upgraded to a twinview GeForce2 MX card and added a second 17" monitor, and am very happy. The second monitor is great for housing the taskbar, toolbars, shortcuts, etc. and monitor download windows, etc. Being able to put 2 full-size browsers or 1 email/1 browser, etc is great, IMO. Counterstrike runs great on the primary monitor, and the mouse doesn't go over to the other one unless you are in a menu screen, so that is a non issue. With MS Flight Sim 2000, I can put the kneepad, GPS display, radio stack, etc. over on the second monitor and keep a full screen for the instruments and view, which helps a ton. (I'm a real pilot and use the sim for some practice, not many people may do or need this...)
The 19" prices are coming down, but I still think dual 17" is better bang-for-the-buck, if you have the desk space and don't need to move them often. If I were still in college, I might re-think it, though. Sam's Club has a great KDS 17" true-flat trinitron tube monitor for $200. Hard to beat! Now, dual 19" . . . hmmm.