Keep away from the "no-make" brands of HDTV because quite frankly, they suck!
Stick with the more common brands such as Panasonic (pricey but fantastic, best on the market featuring the best in sound and picture), Philips, Samsung (great picture, poor sound), Toshiba, LG and even Sony aren't doing too bad now with their latest.
Whats the difference between cheap tvs and the more expensive ones? A lot actually. With the cheap brands, they dont use any picture enhancement technology to make the picture look good, whereas big companies spend a lot of time in developing technologies that really help the way it looks. This includes color levels, contrast (one of the biggest issues between tvs, as cheap brands struggle to get good black and white levels where black actually looks grey - rubbish!), gamma, sharpness and all that stuff.
Panasonic have their V-Real engine, Samsung has DNiE, Philips have Pixel Plus and Perfect Pixel and so on....
If you're looking to spend between $600-900, you can easily get hold of a decent tv, have a look to see what Best Buy have to offer, as you'll find companies like that tend to have the latest ones, then after compare the prices with sites such as Amazon.com to save a bit of money if you were looking to buy off the net.
As for 1080p, yes the 360 can support it but only through VGA and HDMI and only some of the newest games actually support true 1080p, a lot of other games will be 1080i or 720p and so you wont get the true native resolution of the screen but it wont affect the quality of the game youre playing. Obviously if you do get a 1080p tv, you'll not only benefit from 1080p games, but your movies will be upscaled to that resolution too. You will see the difference, people who don't see the difference are not looking properly!
As for the digital cable you're interested in, it might be worth investing in a 1080p. Even though you can still benefit from the HD programming with a standard HD tele, like you said its more futureproof to have a 1080p tv. Im not sure about what sort of HD programming is available in the US as im from the UK, and as far as i know you guys are ahead of us in terms of TV broadcasts. Anyway theres a few ways we can get HD programming, and the most common over here is satellite (
Sky) where HD programming can only be at the maximum res of 1080i as the bandwidth needed for 1080p is way too high for satellite to handle. However with the cable services we have it is possible as its through fibre optics. This proves it will become popular and is still worth getting a 1080p tv even if you don't use that resolution the whole time.
So if you will be watching general television with it too, thats another reason to go for a good brand. Go and have a look at some in stores and ask to compare a cheap one with a better one, you will see the difference.
Hope I've helped a bit =)
Feel free to ask any questions, I should be able to answer most of your TV related queries.
Thanks, Athlon