Today I take my lead from a Reuters article that describes two alternative display technologies that may some day replace (or at least augment) LCDs in mainstream computer systems.
Both are on the market today. OLED (organic light-emitting display) technology, used on some cellphones, creates what amounts to an array of tiny LEDs. This approach is theoretically superior to the way LCDs work, which is to combine a white backlight with colored filters and tiny shutters (the liquid crystals) for each pixel. All the light generated by the OLED is visible to the user, but most of the light in the LCD is stopped in the color filters or the liquid-crystal shutters. If you're looking at a predominantly black image--for example, the main page of Apple.com these days--you may be seeing less than 10% of the light coming from the LCD's backlight; the rest just turns into heat.
The other approach discussed in the Reuters article is what it calls bi-stable displays, after the earliest form of this technology in which the display elements could be set to black or white. Perhaps you've seen these displays in old airports and train stations, where relays would flip dots the size of dimes from one state to the other. Today's version of this technology uses microscopic white spheres in tiny capsules of dyed oil-- in what is known as electrophoretic displays-- or other techniques. They retain their state, but most can display shades of gray, too. A more generic name is "electronic paper," and fittingly such displays are used in electronic book devices such as Sony's PRS-500 Portable Reader System. The Reader uses an electrophoretic display from the E Ink Corporation with 166 dpi (dots per inch).
I have a Sony Reader myself, and I use it a lot, but this generation of display is a long way from looking like paper. The contrast ratio is much lower because many of the capsules appear to be stuck in their white or black states. Also, although the individual capsules are much smaller than a pixel, the pixels on the Reader are much larger than a dot from a laser printer or inkjet. The large pixels makes the text look blocky.
I'm looking forward to the day when the pixels themselves are much smaller than we can see-- when instead of 166 dots per inch, displays have 600 dpi or more.
Some people say there's no need for that kind of display resolution, but just recently we've seen another story about how displays are a long way from good enough. When Apple released its Safari browser for Windows, it came with Apple's own font-rendering engine, which produces very different results from Microsoft's standard renderer. Joel Spolsky blogged about the differences (here) last month. Although I disagree with his conclusion about which approach looks better, my point here is that they're different. With much higher display resolutions-- at least three or four times higher in each direction-- both engines would produce the same results and everyone would be happy.
There are two more related display types that might show up eventually, but they're more of a longshot. FEDs (field emission displays) and SEDs (surface-conduction electron-emitter displays) consist of many tiny cathode-ray tubes, just like old-style CRTs-- but displaying only one spot each. FEDs use many of these per pixel; SEDs use just one.
My guess is that OLEDs will eventually win out in portable applications where rapid updating and high color fidelity are needed (laptops, video players, etc.). Electronic-paper displays may find a niche in e-book readers, but if OLEDs turn out to be as efficient as theory allows, they may sweep the category.
In desktop displays and televisions, where power consumption is not so critical, it's likely that all of these techniques will continue to compete for a long time to come. In these applications, manufacturing cost is the most important thing, which is why CRT-based TVs are still common today.
Display technology has fascinated me ever since I took a job as an engineering manager at SuperMac Technology in 1990. If I recall correctly, my home computer at the time was a 286-based PC clone with a 13" EGA display. At my new job, they sat me down in front of a Mac IIcx with a 19" CRT driven by a true-color accelerated graphics card, and I was instantly hooked. You couldn't even attach displays like this to a PC back then.
Today, displays are a lot better, but there's still plenty of room for improvement-- another 17 years of progress and then some. Keep your eyes open...