nice link - good old wiki. bottom line, there are three main technologies:
TN - mass market LCD displays; low cost, least viewing angle, and refresh times are fastest
IPS - higher end/cost (fewest models available), best resolution, color, and viewing angle, but refresh times are longer
VA - midrange cost, better resolution/color/viewing angle than TN, but refresh rates tend to be the longest (also reports of video input lag; disastrous for gamers!)
if you're concerned mainly about gaming, then TN is the way to go for the fast refresh rate and you're only worried about viewing it dead on by a single person. IPS are for graphics work and can easily cost twice as much as TN. You can get a lot more monitor (screen size, refresh rate, contrast ratio, features) for your dollar with TN, which is why it's still so popular.
TFT is the basic technology of LCD's. TN, IPS, and VA are various flavors of TFT, and each have their own sub-flavors. These effect the color, contrast, viewing angle, refresh rate, and resolution.
LED only has to deal with how the display is lit - these are replacing the old flourescent tubes, which makes them thinner and cheaper to manufacturer. But purists complain that using LED's loses color and creates uneven backlighting (brighter nearer the LED's). Then you open up various types of LED (edge lit versus local dimming). Edge lit is the most common since it's cheapest to implement.
an led = led lcd
it's not a question of either/or. buying an led is buying an led lcd. a non-led lcd uses the old type bulb to backlight it. my personal preference was to get the non-led lcd for the more uniform lighting and better color. i did not mind the thicker and heavier display. i use mine for graphics work and gaming.
frankly, i don't think LED/non-LED should be the main focus when you're shopping for an LCD - focus more on size, resolution, refresh rate, contrast ratio, and cost. features like built-in speakers, USB ports, card readers, and tilt are not as important if you're needing a gaming monitor.
whats your budget and desired screen size? does your PC support HDMI, DVI, and/or VGA? Do you know what your graphics card is? No point in getting a monster display that your GPU can't support. I can look up a few models for you.
for 21.5", I wouldn't worry about LED backlighting issues, so go for the LED LCD you've got in mind. besides refresh rate (and you're right, 120hz is not needed), make sure the response time is <8ms - that's how quickly each pixel changes; lower is better.