You really need to tell how far you are going to sit from TV rather than how big your room is, I can say I am in a 14x24 with speakers out almost 4ft from wall so I have 20ft left over, I sit 11 feet away and I run a 90 in screen with a Projector. If you have no issues with light control I suggest you look there, my 720P HD Panasonic unit and budget screen was only $800 and thats cheaper than most budget units of 42 and certainly above.
If you google HD screen size and seating distance it will give you an idea of ideal size to look for, with HD units and signals you go as big as you can within reason, not like the old days where you had to sit so far back for proper picture to avoid seeing pixels.
