1080i and 720P are about equal, except 720P can have a better response time which is the choice procast signal from ESPN or other stations that need a quick response time to avoid a choppy images. I find that 1080i is the best for nature programing such as Discovery HD, or programs where the camera doesn't jump from place to place such as a football or tennis game. On some HDTV's that are listed as 1080i, you can get a picture that is almost comparable to 1080P and difficult if not impossible to tell the difference in picture quality.
Note: All HDTV prodcast are in 1080i or 720P. You can only get 1080P through Video Games or HD movies played on an HD dvd player or Blue Ray. HD movies can also be viewed in 1080i by using an Upconversion DVD player, which is a lot less expensive than the Blue Ray or HDDVD players. Look for specials with a price of $100 or less on upconversion DVD players.
I recommend a "Response Time" (RT, MS) 8 or below................. The lower the better for fast or quick action. The best TV's have 8 or less, as the cheaper sets are above 8 , and have an inferior picture quality.
A Contrast ratio of 1600 or better................. Higher is better because you get a clearer the picture. Better contrast between true black and true white. Remember that the picture you see in the store may not be the picture quality you receive at home. There are some really good LCD's on the market at competitive prices (37-42 in. under $1000) Once you experience HDTV you wouldn't want to go back to the old CRT.
NOTE: Beware of the new glass panal (sscreen) LCD's. They are cheaper to make, but are not as good for viewing as the original.
I also recommend purchasing the extended warranty.
Input-Output
Optical out...(I found that the optical out was handy for conecting to my 5.1 sound system.)
USB ..(connection for updates from manufacturer, such as with the new Olevia 237V series.)
HDMI 1 ( you can always add on an HDMI dock with 4 or more slots for uder $100)
VGA......( in case you don't have an HDMI to dedicate to your computer. I can use my computer's Media Center to show pictures, movies or documentaries that are on my hard drive. Great if you have a wireless keyboard and mouse because you can also review e-mail as well as write e-mail using your LCD TV as your computer monitor.)
All LCD TV's have connection for TV , coaxil for Video player, and RCA for Surround sound outputs.
http://www.tigerdirect.com/ is a good place to comparison shop, without any sales tax and sometimes free shipping.