There aren't really any terrible TFTs on the market. Some a only okay-ish, but probably still better than what you have now.
The two brands to buy are Samsung and LG.
The huge price differences come from different panel technologies. All cheap TFTs use TN panels. That's the normal stuff - very fast reaction time but the colors aren't "real" enough for professional graphics artists. That's perfectly fine for gaming.
But the guys who are paid to know exactly which color of their color table they use for their project need a monitot which (a) offers a color space similar to reality (and print) and (b) can be calibrated to make the fit 100% if possible. As you can imagine they're charged quite a premium. These monitors are often too slow for gaming, at least for shooters, but their image quality is absolutely superb.
There's also another panel in-between. Better, more "real" colors than TN, faster than the pro stuff. How fast TFTs based on such a panel are has to be checked for each model. Maybe it's fast enough for gaming. Their image quality is also better than on TN panels. The price maybe only twice as much.
The differences in speed and image quality can actually be seen. They're not just theoretical numbers.
As you can see the choice is not easy.
Things you should know before you buy:
1. panel type (not mentioned means TN)
2. LED backlight, etc. (many new technologies in the last 12 months)
3. pixel error class (maybe even the possibility to return the product at your convenience)
4. input lag (how long the TFT "thinks" before doing what it should; very important for gaming)
5. is the monitor silent or does it make a humming sound (most TFTs do the latter!)
You can either spend a lot of time finding the relevant infos or you simply browse a dozen games sites and write down their top 10 lists for monitors. I know the German print mags have such lists on their sites and update them every month.