When it comes to LCD vs LED, there really isn't much difference, and it won't affect your gaming at all. The difference between LCD and LED is the type of backlight used. Both displays use LCD technology to actually put the picture up on the screen, but monitors labeled "LCD" use cathode backlights where LED monitors use LED backlights. You're going to want to go with an LED monitor, because it's going to give you a better contrast ratio, and you won't get as much light bleeding through the screen as you would with a normal LCD panel. This means you're going to have darker blacks and brighter whites without having any light bleeding through the edges of the screen. An LED monitor will also use less power.
Long story short, definitely go with an LED monitor.
The thing you really have to look out for when gaming is the response time. Generally, you're going to want a monitor with a 5ms or lower response time. 2ms is going to be the absolute best, although I have seen a few 1ms monitors out there.
Now, if you want to have the best picture possible, then I would suggest going with an IPS panel. IPS panels give you much better color accuracy and a much larger viewing angle than normal LCD or LED TN panels. One issue with IPS panels, however, is that you start to see slower response times. I personally have an IPS panel that is rated at 6ms, but I can't tell the difference between that and my old 2ms LCD.
Also, you might want to consider getting an even higher resolution. At 27 inches, you start to see many monitors with a 2560x1440 resolution, which is going to give you an even sharper picture than 1920x1080 (1080p), but the price does start to jump up a little here. Also, 2560x1440 is going to cause your framerate to drop (especially if you don't have enough VRAM) in games a little just because the resolution is so much higher.
If you want a really nice 1080p monitor that's going to give you amazing colors and viewing angles then I would definitely suggest this one:
If you can spend a little more, then you could always upgrade to 2560x1440 though. This is the one I'm using (fyi: I did have to adjust the colors quite a bit when I first got the monitor, but they're amazing once calibrated correctly):
You could also go for something from Overlord Computers, but it looks like they're sold out right now. They're definitely something to look out for though:
If you're really loaded then you could always go with a Dell U2711, but I really don't like the anti-glare coating on the screen. I feel that it washes out the colors a bit:
You could also go with a Yamakasi, Catleap, or Achieva Shimian monitor, but those IPS panels are pretty bare bones monitors (many come with only a power button and a single input port), and you're not going to get a warranty with them. Logan did a review on the Achieva Shimian a while ago: