I would recommend a plasma over an LCD. They're a bit cheaper for a larger size compared to an LCD. I actually perfer the picture on a plasma (more like a traditional TV) over an LCD.
I believe the smallest plasma is 42in but you should get the biggest one that you can based on the room size and viewing distance. The "viewing rule" is 2.5 to 3 times the diagonal size of the TV. For example, if your viewing distance is 8-10 feet, the TV should be no smaller (or much larger) than 42 inches. Or to reverse that, if you get a 50 inch TV, you should sit about 10-12 feet away for it.
The main thing to remember is that flat panels are usually wide screen. When you view a traditional TV program on it, it will have black bars on the sides or (if the TV has it, most do) the TV will "stretch" the image to fit the screen. This will slightly distort the image but you will get used to it.
Another thing to remember with flat panel TVs (LCD or plasma) is that they may (and usually do) show regular (not DVDs or HDTV programming) slightly worse than an old style (tube) TV.
While they usually cost a little more, look for TVs with a built-in ASTC (HD) tuner. If you live within the recieving distance of your local stations and have get a small antenna, the HD picture will be STUNNING! HD TV from cable or satellite and DVDs will be very good too. Make sure to use the best connections (not the wires, the connectors. There are 3 or 4 basic types) from the cable or satellite box or the DVD player.