Here are a few hints on how to choose a monitor:

1) Display technology

Nowadays there are basically three types of displays being used in monitors: TN, IPS and PVA. You can google details about all three, but here's the basic break down:

TN is cheap crap used in 90% of all monitors, popular in consumer devices sold in supermarkets and such. It has only two advantages: it's cheap and it has very fast response times, which might be of some value if you're much into gaming. Apart from that, it's crappy viewing angles, pathetic color reproduction and a backlight that will burn your eyes dry. BTW, if a device description doesn't tell you what kind of display it uses, it means it's TN and they prefer not to disclose. Also, if it has 2 or 3ms response time, it must be TN.

IPS and PVA is the stuff of people who know what they're buying. Great colors, great viewing angles. IPS are generally better for heavily-lit environments (think your typical corporate office), while PVA are better for darker environments (think your home) and easier on your eyes.

There's also one important caveat with regards to IPS. "Classical" IPS is no longer made, the technology has evolved over the years and now it's stuff like S-IPS, H-IPS or e-IPS. So whenever you see IPS, it means you need to dig deeper into the tech specs, because it's going be some variant of IPS. And that is important, because in the recent 12 to 18 months the market was flooded with e-IPS displays, which are basically a cheaper, but simplified, and thus an inferior version of IPS. Which is still better than TN, so you might go for e-IPS as an economical choice, but you need to be aware of the trade-off.

2) Display surface.

Maybe it's a matter of taste, but in my opinion always go for matte over glossy. Glossy looks good in a store, because it seems clearer and the colors seem a little more vivid. And most customers, like children, go for the tasty Skittles, and not for the healthy fruit. But I find it to be an annoying compromise in terms of viewing comfort, because everything will reflect in a glossy screen. And I'm not talking just about bright light sources (like lamps or sun), but literally everything, even if in a much subtle way than a light source. That means, with a glossy screen you always get your screen picture polluted with subtle shades and shapes from your environment (including your ugly face ;).

3) Working space and orientation

Obviously, you'll want as many pixels, as possible. In my opinion, 1920x1200 is an absolute minimum. Now, the important question is how do you organize your virtual environment for your main work (i.e. programming, I assume). Do you work in a single text-editor window (say, Sublime Text 2), or an IDE? Or multiple texts side-by-side? If it's a single text window, I found it's very helpful if you can see as much of the code as possible (for better context awareness and browsing efficiency) which means putting a 1920x1200 monitor in portrait mode. So in that case you'll want a monitor with a pivot.
If you can afford it, get two 1920x1200 monitors or one 2560x1600 (I guess 2560x1440 will do too, although I hate 16:9).

4) Manufacturers

Well, there are the popular, reasonably priced, medium quality manufacturers, like Dell or HP - the Fords and Chevies of monitor market.

There are the cheap alternatives, where either you consciously buy something lower quality for lower price or you do your research and find a little-known underdog that produces something decent. In that group I'd put all the Hazros, ASUSes and Hannsprees of this world.

There is the Jaguar of monitor market, i.e. Apple, which makes an overpriced product (very decent quality, but not mind-blowing). But some people fall for the looks, are blind fan-boys or most likely go for the popular image because they need the ego boost, to feel more sophisticated or artsy.

And then there are the Mercedes and BMWs of monitor market: NEC and Eizo. Those are of high quality and neat, understated design. Their higher models are basically the golden standard for professional graphics designers. Eizo has a slighter leg up in quality, but for me personally NECs look better with that black, rectangular shape, like the old-school ThinkPads (while with closed lid ;). Also worth noting, Eizo manufactures its products in Japan, not in China, like the rest of the herd.

5) Monitor reviews

Steer clear of popular, general IT/tech sites, like CNet or Engadget. These people will tell you about the input ports and parameters they've read in tech specs and give a vague impression of picture quality. Some have even heard of the different panel types, so will knee-jerk to praise anything IPS. But they don't really have a clue how to judge a monitor. Their reviews are as good as if you asked your buddy or neighbor about his display, but with nice photos.

For more valuable advice, you have to visit sites that are capable of making technical evaluations. Good starting places are probably TFT Central, Prad.de (there's an English version) and AnandTech.