Most of the led lcds and ccfl lcds seem to be maxing out at around 300-400 lines of motion resolution without motion processing enabled. Many people have problems with motion processing due to artifacts or just the way it looks. Generally if you pay more for an LCD you will get a higher motion resolution of around 600 lines without processing.
Plasmas can usually hit around 900 lines for 1080p models. Current 720p Plasmas aren't actually full 720p, they cut the horizontal res from 1366 to 1024 to save money and lower power draw.
Plasma will show some phosphor lag though where the color sub pixels don't change at the same rate.
Input lag will be a big factor for you as well, Plasmas generally do very well while lcds can lag behind when motion processing is enabled.
Input lag measurements can be found on the web, usually in a list format.
For the 400-600$ price range Sony, Samsung and Toshiba led lcds are good choices for overall picture quality. Samsung and Panasonic are the 2 best brands for Plasmas in the price range. Panasonic is probably a little better but also usually more expensive in the low end.
For 800-2000$ The Panasonic Plasmas like the st50 have a strong advantage. If you don't need an anti reflective filter you could move down to a ut50 or u50.
Vizio's 2012 led lcds are also very good for the price and available in a smaller screen size, but they fall behind the Panasonics in a few areas: http://reviews.cnet.com/flat-panel-tvs/vizio-m3d470kd/4505-6482_7-35159744.html
Cnet.com is a great place to find measured performance like motion resolution of various tvs.