Regardless of what type of monitor you're considering, size is a priority. A bigger monitor offers easier to read text, better graphics and the ability to have more and larger windows open on your desktop. All monitor sizes are measured diagonally across the screen, but that number isn't the true viewable area. The plastic frame around the monitor hides a certain amount of the screen so there is a difference between the quoted size and the actual viewable area. A monitor's viewable area should be within an inch or so of the quoted size.
The standard monitor size used to be 15 inches, but 17-19 inch monitors have become the norm as prices have decreased. You can get a 17 inch CRT starting at $300. An adequate 19 inch CRT can be had for $400 but better quality will cost more. If you need a large screen for group presentations, a 29 inch monitor will cost a few thousand dollars. You can get a 29 inch PC/TV hybrid monitor for about $1000, but these monitors have low resolutions and are unable to produce high-quality images.
A LCD is about double the cost of a CRT with a comparable viewing area. The minimum size you should consider for a LCD is 15 inches with prices starting at $600. Larger LCDs go up in price from there with an 18 inch monitor costing around $3000. Buying a flat panel display will definitely leave your wallet flatter too.
A factor for both CRTs and LCDs is resolution. The number of pixels horizontally and vertically defines a monitor's resolution in pixels or dots per inch (ppi or dpi). The greater the resolution, the more information or image you'll be able to view at once. The average user will find a resolution of 1024x768 more than sufficient for everyday work. You can achieve this resolution on CRT monitors 17 inches and larger or LCDs 15 inches and larger. Keep in mind that CRTs can display multiple resolutions, but LCDs are optimized at only one resolution.
Monitors can come with a variety of extras. Some have built-in speakers or jacks for microphones and headphones. Other monitors have dual inputs so you can connect two computers to the same monitor. With the advent of USB (Universal Serial Bus), some monitors have USB hubs at the back, allowing you to connect more peripherals. You can also get accessories like anti-glare filters and specialized mounting stands that help minimize glare and provide a comfortable working position.
To keep your utility bill down, you should look for a monitor that is Energy Star compliant. Energy Star is a program developed by the US Environmental Protection Agency (EPA) to make energy-saving office equipment like computers and monitors. An Energy Star monitor automatically goes to sleep or powers down after a period of inactivity. This feature can save 60-80% of power during idle times. All you have to do to wake up the monitor is touch the keyboard or mouse.
The majority of monitors are certified as "low emission" since they meet standards like MPR II or TCO. These guidelines were developed in Sweden (the acronyms are Swedish too) by a number of organizations to set limits for electric and magnetic field emissions. The newer TCO standards are the strictest. So if you're concerned about emissions look for MPR II or TCO certification, not just the words "low emission."