As pointed out, you cannot exceed (go beyond) the native screen resolution of an LCD monitor. Therefore, it is important that you invest in an LCD monitor with the highest screen resolution you will use. You can run them at lower screen resolutions if you want to but, depending on the LCD monitor, some degradation can be noticed. However, I have not had any problems with my screen when it comes to this. I run it at its native screen res for everyday work, etc, and only let this change for some games that require a lower screen resolution.

I would get a large LCD screen with a high screen resolution. I am running a 24" LCD that has a screen resolution of 1920 x 1200 (wide screen format). Besides the screen resolution and overall monitor size, the next important thing to consider is the monitor's refresh rate. The faster (the lower the number) the better. I have not had to look at LCD screens in almost two years, so I don't know what the refresh rates are at now, but lower cost monitors tend to have worse refresh rates. This is one area you don't really want to skimp on. Refresh rates tell you about how quickly the monitor can refresh each pixel on the screen. If the number is high (a poorer refresh rate) then you can see "ghosting" when something is moving on the screen. This is very important when you are playing a game, modeling in a 3D app (and moving or rotating an object) or even watching a movie. Ghosting is when you have a sort of blur from frame to frame which, frankly, gives me a headache. If the refresh rate is high enough then you get little to no ghosting at all.

I would shoot for at least 8-12ms for the refresh rate. If they have faster, great, but compare prices and refresh rates for each monitor. If the refresh rates get up to 16ms or higher, then I would forget the monitor and find another. However, refresh rates are a strange thing. Like benchmarked software, companies tend to use a variety of means to determine refresh rates and then list the best result (ignoring the poor results). Therefore it is possible for one monitor to have a poorer refresh rate (i.e. 12ms) and actually outperform one rated with a lower refresh rate.

Before buying your monitor you should research and compare the specs for each monitor looking for the things I listed above (max screen resolution, monitor refresh rate and overall monitor size) and a few other things such as the viewing angle, etc. Then, after narrowing it down a bit, I would read a lot of reviews to see if anyone is mentioning any problems or complaining about a monitor's refresh rate, etc. Places like Tom's Hardware, etc, tend to review hardware, putting them to the test and telling you about the pluses and minuses.

I hope this has helped a bit.