I am very happy with the SD picture on my 50" Panasonic, especially if you view in 4:3 mode. The "just" mode to fill the screen does not distort as badly as the full stretch that some TVs offer. HD is outstanding.
My budget is around 2300.00. I was wondering which tv in that price range had the best picture with a non-HD signal. I will have hd but just curious.