If you're looking for "bang for your buck" get a DLP. My Samsung is a 120hz, 1080p, 50" DLP and I paid $1000 for it. It was marked down. It's got three HDMI inputs, two optical audio inputs, a PC input, plus plenty of the normal RCA and RBG hookups. The picture is better than a 120hz 1080p LCD. I compared mine with a Sony Bravia with the same specs just hooked up to Direct TV and the picture on the DLP was better. As far as 1080i vs 1080p goes; P is always better than I. They stand for progressive scan or interlaced. It's just the way the screen refreshes. A TV with 1080i has almost the same picture resolution/quality as a TV that is 720p. Don't even waste your money on a TV that's less than 1080p because you'll regret it as soon as you see a TV that is 1080p hooked up to a BluRay.
As far as brands go, almost anything Jap is better than anything Korean or American. If you're going to go with an LCD, Sharp makes the best LCDs on the market, probably followed by Sony, Samsung, and LG. Some other companies out there make a good product as well, like Phillips and Panasonic, but I would rather pay a couple hundred more bucks for a much better TV.
I'm bias toward DLP. They're cheaper and better quality. If you decide to go with a DLP, I'd shy away from Mitsubishi. My dad has a two year old Mitsu 1080p and he's had to change the bulb three times and his fan has problems. But the picture on his Mitsu isn't as good as my Samsung because his is 60hz and mine is 120hz. Mine is also brand new.
If you really want to do some research and get the facts for yourself, go to
www.avsforums.com and read some of the stuff there. Avs=audio video science. Great site.