1. Native resolution. This resolution corresponds to the number of physical pixels that comprise the panel. This is the resolution at which the display has it's best image quality. Unfortunately, LCD displays do not span resolutions like a CRT, so there will be loss of image quality or size, depending on how you plan to configure the panel for non-native resolutions. Your two options when running non-native resolutions will be to have the image fill the screen and lose image quality, or have the panel only use the pixels that correspond to the resolution you have selected. This will result in borders on the top/bottom, sides, or both; for example, running 1280x1024 on a panel with a native resolution of 1600x1200 will result in borders around the entire image, but will not result in IQ loss.
2. Panel type. They can be broken down into additional sub-categories, but for all intents and purposes, the main categories are IPS, MVA/PVA, and TN. TN panels are what comprise most LCD panels, especially those claiming very low response times. They are the least expensive to manufacture, but they also have the lowest viewing angles, have the least accurate color reproduction, and least amount of uniformity. IPS panels are the best quality in that they have the best viewing angles, best uniformity, and the best color reproduction; this is due to the fact that they are true 8-bit panels, where the others are 6-bit w/dithering. MVA/PVA panels are the best compromise. They offer good color reproduction and good response times. Kind of a jack of all trades, and master of none.
3. Brightness ratings aren't that big of a deal. Most monitors you find will likely have a CDM2 (nits) value of 250-300.
4. Contrast is the big one. Contrast refers to the difference between the darkest dark, and lightest lights. The higher this value the better. Panels with low contrast ratios have a hard time reproducing blacks, and it tends to come out somewhat purple. LCDs still don't product blacks as good as CRT displays, but this is a shortcoming of the way they use CCFL back lighting.
5. Response times. These are often convoluted because of the way the manufacturer took the measurement. Some times the numbers are gray-to-gray, and some times they are black-white-black; some times they may actually tell you both. However, keep in mind that response times are not fixed values and can fluctuate. Some lower quality panels may claim very low response times, like 4ms, but when under harsh loads where much of the screen must change drastically, they can actually jump up to well over 20ms. So, always take response times with a grain of salt, and see if you can find any reviews on monitors you may be considering.
6. Input options. Many of the lower cost LCD panels still have only analog D-Sub inputs. LCD panels are digital devices, unlike analog CRTs, so they do have noticeably better image quality when using DVI over the analog D-Sub; this is especially true when viewing text. The few extra dollars you may pay for a unit with a DVI input will be well worth it.
7. Warranties are not all the same. Many lower cost LCD panels come with only a 1-year warranty. The better products will include 3-year warranty, but check the fine print. Make sure the warranty includes back light coverage, as that is separate from the LCD panel itself. The unfortunate thing is that back lights can often be so expensive to replace that it would cost nearly as much as you paid for the monitor.
8. Pixel policy. Although this could have gone under the warranty section, the pixel policies tend to vary so greatly among manufacturers, even when the general warranty is the same. You may find that many companies don't post their pixel policy and you have to ask for it. DO IT!!! This will let you know how many full pixel faults (black or white dots) and/or sub-pixel faults are required before they would replace the panel under warranty. Their policy should not only outline the number/type of faults, but location on the screen and proximity of faults to one another.
Odds & Ends:
Height adjustable stands. Some monitors have a stand that allows height adjustment, which may be helpful when configuring your monitor based on your computer desk and chair height configurations. Not all monitors have them. Some have only a tilt option and the height is fixed.
Pivoting screens. This feature is even less prevalent. This allows the monitor to rotate from the standard landscape mode to portrait mode. This can be handy if working with documents that are in legal type format, or documents that are very long, but not very wide.
USB ports. Some higher end monitors will include a USB hub in the monitor allowing for a couple of USB ports in the monitor itself. This can be very handy for connecting things like memory cards, mice, keyboards, or other USB devices which may be installed/uninstalled often, or have cords that may be difficult to route to the back of your computer.
I think I've hit the major points, but I'm sure some else can post some additional items for consideration.
2. Panel type. They can be broken down into additional sub-categories, but for all intents and purposes, the main categories are IPS, MVA/PVA, and TN. TN panels are what comprise most LCD panels, especially those claiming very low response times. They are the least expensive to manufacture, but they also have the lowest viewing angles, have the least accurate color reproduction, and least amount of uniformity. IPS panels are the best quality in that they have the best viewing angles, best uniformity, and the best color reproduction; this is due to the fact that they are true 8-bit panels, where the others are 6-bit w/dithering. MVA/PVA panels are the best compromise. They offer good color reproduction and good response times. Kind of a jack of all trades, and master of none.
3. Brightness ratings aren't that big of a deal. Most monitors you find will likely have a CDM2 (nits) value of 250-300.
4. Contrast is the big one. Contrast refers to the difference between the darkest dark, and lightest lights. The higher this value the better. Panels with low contrast ratios have a hard time reproducing blacks, and it tends to come out somewhat purple. LCDs still don't product blacks as good as CRT displays, but this is a shortcoming of the way they use CCFL back lighting.
5. Response times. These are often convoluted because of the way the manufacturer took the measurement. Some times the numbers are gray-to-gray, and some times they are black-white-black; some times they may actually tell you both. However, keep in mind that response times are not fixed values and can fluctuate. Some lower quality panels may claim very low response times, like 4ms, but when under harsh loads where much of the screen must change drastically, they can actually jump up to well over 20ms. So, always take response times with a grain of salt, and see if you can find any reviews on monitors you may be considering.
6. Input options. Many of the lower cost LCD panels still have only analog D-Sub inputs. LCD panels are digital devices, unlike analog CRTs, so they do have noticeably better image quality when using DVI over the analog D-Sub; this is especially true when viewing text. The few extra dollars you may pay for a unit with a DVI input will be well worth it.
7. Warranties are not all the same. Many lower cost LCD panels come with only a 1-year warranty. The better products will include 3-year warranty, but check the fine print. Make sure the warranty includes back light coverage, as that is separate from the LCD panel itself. The unfortunate thing is that back lights can often be so expensive to replace that it would cost nearly as much as you paid for the monitor.
8. Pixel policy. Although this could have gone under the warranty section, the pixel policies tend to vary so greatly among manufacturers, even when the general warranty is the same. You may find that many companies don't post their pixel policy and you have to ask for it. DO IT!!! This will let you know how many full pixel faults (black or white dots) and/or sub-pixel faults are required before they would replace the panel under warranty. Their policy should not only outline the number/type of faults, but location on the screen and proximity of faults to one another.
Odds & Ends:
Height adjustable stands. Some monitors have a stand that allows height adjustment, which may be helpful when configuring your monitor based on your computer desk and chair height configurations. Not all monitors have them. Some have only a tilt option and the height is fixed.
Pivoting screens. This feature is even less prevalent. This allows the monitor to rotate from the standard landscape mode to portrait mode. This can be handy if working with documents that are in legal type format, or documents that are very long, but not very wide.
USB ports. Some higher end monitors will include a USB hub in the monitor allowing for a couple of USB ports in the monitor itself. This can be very handy for connecting things like memory cards, mice, keyboards, or other USB devices which may be installed/uninstalled often, or have cords that may be difficult to route to the back of your computer.
I think I've hit the major points, but I'm sure some else can post some additional items for consideration.
