Projectors have uses in business and education as well as in home theaters. Since televisions are among the fastest changing electronics, this projector buying guide shows some of the latest options available, so you'll know how to buy a projector that will meet your business or consumer electronics needs.
Before considering what type of projector to buy, you'll need to know how to decipher product description pages. First, projectors use three different technologies:
Digital Light Processing (DLP)

Liquid Crystal Display (LCD)

Liquid Crystal over Silicon (LCoS)

Each technology has advantages and disadvantages; which type to select is usually based on specific features, which are closely related to their price. Features include:
Resolution: The pixel count projected to the screen; technical types use alphabetic designations; consumer electronics vendors use pixel counts (number of pixels, listed horizontal by vertical):
Brightness: Light output determines the visibility of an image in a room. Measured in lumens, projectors range from about 200 to 10,000. If you need to view the image with room lights on, you'll want a projector with a higher lumen count. Home theater projectors rated at 1,000 to 2,000 lumens are suited to a dark room. Business or education users who have lights on during presentations will prefer projectors rated 2000-3000 lumens. Still higher numbers are needed when in very large or very brightly-lit amphitheaters. Many projectors offer variable brightness (a dimmer switch, if you will).
Contrast ratio: Measures the difference between brightest white and darkest black of an image. LCD projectors start around 400:1; LCoS projectors about 600:1 and DLP projectors at 2,000:1. Higher contrast ratios produce more defined pictures: 5,000:1 is very good; 10,000:1 is very impressive; 20,000:1 is very expensive.
There are several ways to use projectors, each with its own considerations:
Mobile presenter
For the salesperson, consultant, after-dinner speaker or others who rarely present in the same place twice, the prime projector consideration is portability. Other points to consider: a variety of connections (cable, computer, wireless), variable brightness and versatility enough to work in a large hall or small office.
Business
Managers and executives in the conference room or boardroom will likely be more satisfied with ceiling- or wall-mounted projectors. Size isn't an issue, but you want the device out of the way. Key points: a quiet fan and good speaker connections; brightness of 2,000 to 5,000 lumens; computer or wireless connection; high resolution (WXGA or SXGA) and high-contrast ratio if technical documents or lots of text will be displayed.
Non-profit
Every year, more schools, churches, libraries and other community groups are using interactive, technology-based programs. Not-for-profit operations always have price (or the name of someone they can hit up for donations) on their minds, so SVGA or XGA projectors will be serious cost-conscious contenders. In fact, basic home theater projectors are good enough for most uses. Mounting or portability will depend on the situation; some groups have just one media room, some will need to use their projector in several rooms in sequence or at the same time. Key points: brightness of 2000-5000 lumens; quiet fans; good connectivity (especially audio); locks or other accessories like those used for computer security.
Home theater
The home theater projector user wants real movie-theater quality; excellent color, detail and sound. WXGA or SXGA resolution is where you should start, and the ability to project big images is a major plus. Key points: brightness above 2,000; contract ratio above 5,000:1; good color saturation; great audio connections. The simple truth for a true home theater aficionado: Spend what you must to get the projector you want and don't look back. Your years of viewing pleasure will long outlast the time you remember the bill.

Lamp
This is a major consideration, as lamps can cost hundreds of dollars to replace. You want a lamp with a long service life. Many projector lamps list 2,000 hours; this is good. Some high-end models list a life of 60,000 hours; this is impressive and pricey. Be sure to take care of your projector lamp to maximize its life and have a spare handy, since no one can know exactly how long any individual lamp will last.
Screen
A good projector screen is necessary for the best viewing. Four basic options are available:

Gain: describes the reflectivity of the projector screen and viewing angle; 1 is comparable to a white-wall type screen. You can find gain as high as 4, though 2 is generally the max. There is a trade-off; as reflectivity increases, viewing angle decreases so you can't sit way off to the side of the projector screen and still see a good image.
Size: Like resolution, this is expressed as a ratio of width to height: Square: 1:1--square projector screens are not very common with projector TVs, but they are available. Fullscreen: 4:3--like a standard television, these projector screens can switch between full and widescreen with very little loss of watchability. Widescreen: 16:9--most high definition television and movies are shot in this format, so get a projector screen that doesn't short-change you with lots of blank space top and bottom.
Do: Wipe the projector exterior clean with a lint-free cloth dampened with a little isopropyl alcohol (or, better yet, a 50-50 isopropyl-water mix) then wipe dry. Get a can of air and blow the dust out of any openings. If the room gets a lot of dust, pet dander, etc., use an air purifier. Consider a dehumidifier if working in a humid climates. (Both are available in the Overstock.com home store!)
Do not: Turn off your projector. (Instead, turn the lamp off, let the fan run until the lamp is cool to the touch; then shut down.) Expose consumer electronics to extreme temperatures or rapid temperature changes. Connect directly to the power grid. (Use power protection--a surge protector and a UPS.)

Some accessories to consider:
What about the projector's weight?
If the projector is wall- or ceiling-mounted, or sits in the same spot in the living room, weight isn't a big issue. Smaller projectors are more technologically advanced, so pricier, but good, lightweight models can also be found on the economy shelf.
Will my projector connect where I need it to connect?
A/V cables and come in a wide variety: Coaxial, Ethernet, FireWire, HDMI, RCA, Toslink, USB--enough acronyms to fill a building with government agencies. As you consider which projector to buy, consider where you might connect it--cable, computer, DVD player, intranet, Wi-Fi--and pick one with the appropriate ports or connection jacks.
See the big picture, hear the small whisper
What's dazzling video without astounding audio? Pick out a home theater speaker system! For small rooms or the budget-conscious, a package containing amplifier, tuner and speakers, known as home-theater-in-a-box, is enough but not too much. For parents who have never shouted "Turn your stereo down!" at their teens, go with surround sound speakers, a multi-speaker system identified by number: 5.1, 6.1 or 7.1; the ".1" is the subwoofer (for deep notes); the other number is how many speakers in the set. Spread them around the room and they'll reproduce theater-quality audio to match the theater-quality video.
Mega-byte the bullet
You can connect your computers and video game consoles to your DLP projector or LCD projector for widescreen viewing of games, web surfing and just about anything else. You won't necessarily have to trade-in your current computer monitor; just switch the cables, if you use the monitor most of the time, or use a simple KVM switch to run both computer and projector from the same keyboard and mouse.