Display Technology

Some gamers view 40" is the 'new' 28". If your buying a HDTV for gaming then this is the size that you want to aim for or above. But be aware that larger screens require more eye movement depending on how close to them your sitting, so a 50" screen may actually make you worse at twitch reflex based games like FPS's if your too close to it. However in the case of driving games bigger is probably always better :).

LCDs

Brightest images, no degradation over time, 30% (?) cheaper in energy costs over plasma. Prices set to drastically during 2007 resulting in 42" screens potentially dropping to $999. LCD technology has higher potential resolutions then Plasma technology, and has been truly embraced by the computing industry.

Plasma TVs

Plasma display technology is not popular with PC or laptops users, to the extent that 95% of flat screens are LCD based. Phospherous gasses escaping causes these screens to get continually dimmer over their lifetime even when switched off. Cheaper the LCD. Superior black levels in picture quality, but not pleasant to view in direct sunlight, or as bright as LCDs

DLP

Biggest screen size other then projector for your money. Bad at viewing angles.

Projectors

Most cinematic as you can have truly huge images. Not necessarily an advantage for online competive games where you need to look at your health, minimap and targeting areas of the screen. Requires expensive bulbs to be changed (in some cases they get dimmer). Be aware that even the super expensive state or the art projectors used in cinemas cannot show vivid images without the lights turned off. Of course when the lights are turned off they are cinematic by definition :)

Video Gaming