In this test I carefully lined up an ISO resolution test target only using the optical viewfinder of each camera.

The red shaded area represents the viewfinder coverage. I have computed the number of pixels represented in the viewfinder and the percentage of the total image pixels.

Canon EOS-350D (Digital Rebel XT in some markets)
The viewfinder is slightly offset to the left.

Total image size: 6456x2304 pixels = 7,962,624 pixels
Viewfinder coverage: 3264x2176 = 7,102,464
Percentage viewfinder coverage: 89.2%

Konica Minolta Dynax 5D (Maxxum in some markets)
There is quite a noticeable displacement towards the bottom of the frame here.

Total image size: 3008x2000 = 6,016,000 pixels
Viewfinder coverage:2860x1902 = 5,439,720
Percentage viewfinder coverage: 90.4%

Nikon D50
Good coverage, but the viewinder is slightly rotated.

Total image size: 3008x2000 pixels = 6,016,000 pixels
Viewfinder coverage: 2887x1921 pixels = 5,545,927 pixels
Percentage viewfinder coverage: 92.2%

Olympus E-500 (EVolt in some markets)
Note the E-500's taller 4:3 aspect ratio compared to the others.

Total image size: 3264x2448 pixels = 7,990,272 pixels
Viewfinder coverage: 3072x2304 pixels = 7,077,888 pixels
Percentage viewfinder coverage: 88.6%

Pentax *istDL
The Pentax *istDL is the clear winner with a straight view and the best coverage.

Total image size: 3008x2000 pixels = 6,016,000 pixels
Viewfinder coverage: 2892x1926 = 5,569,992 pixels
Percentage viewfinder coverage: 92.6%