Every once in a while, I get an inkling to window shop for HDTVs. However, I always run into the same problem when I try to compare screen sizes of different aspect ratios. The standard 4:3 sets usually come in 20, 24, 27 and 32 inch diagonal sizes. The widescreen 16:9 sets come in 26, 30, 32, 34, 37, 42 and larger diagonal sizes. Since the ratios are different, there's not a direct correlation to the diagonal measurements, and I never knew whether stepping up to a wider widescreen would actually result in a picture bigger than our current square screen.
Just today, I discovered that the folks at C-net have come up with a screen size calculator that lets you determine the effective size of a 4:3 image on a 16:9 screen and vice versa. Now I know that if we get a 30" diagonal widescreen TV, a 4:3 picture on it would be the same size as a 24" standard dimension television.