Fully agree with Dapper Dan. By the way, why have you ruled out plasma? The burn-in issue has largely been solved and picture quality is usually a tad better than LCD flat panel.
On the whole it really depends on how and what you want to use the TV for. As Dapper Dan pointed out, projection systems sort struggle with the light output.
Concerning the TV's themselves, look out for connectivity options (number of HDMI, component inputs etc.), native video resolution, and video features/enhancements. In terms of video performance check out how you like things like DNiE (Samsung), Wega (Sony), PixelPlus -2 (Philips), etc.
I would suggest that you take your favorite DVD to the shops and have them play it on the TV's. Particularly watch for how the TV deals with fast actions scenes, diagonals, and contrast. Try to make sure that the other TV's are turned off and you are watching only one with the brightness set to a "normal" level. Usually what deals do is turn brightness to the max because a TV that is brighter seems to attract more people. Once you take it home the first thing to do is adjust the brightness otherwise colors will look "washed out".
Note that all flat screen TV's will look absolutely stunning with animated content (Finding Nemo for example) but have noticeably more trouble with "real persons".
Last but not least, have the dealer display regular PAL/NTSC content. Chances are, this will be what you watch a lot too and if the TV doesn't display this properly you will be frustrated with what all your money got you.
Good luck.