I've been looking into this recently, and as the other posters have mentioned, you can't compare the H-IPS panel of the LED ACD with cheap TN displays that go for $200.
The LED ACD with have:
- better color rendition
- better color consistency
- better viewing angles
- brighter
The only advantage of the TN displays is lower lag. So if your only application is gaming and you need to cut those precious 10ms out of the response time, go for TN. Otherwise a nice PVA (most Dells) or IPS (Apple, high-end NEC, etc) will be much better.
BTW, I got an LED ACD refurb, and it's fantastic (IMHO better than the top end NEC, as long as you don't mind the glossy screen).