Many websites don't scale correctly for higher (higher than 1024x768) resolutions. I've made a fast search (using 1280x1024) and here are my findings.
Not computer related news sites usually don't scale well. Examples: gazeta.pl (Polish daily) - empty area at left and right side of the text (it's approx 800 pixels wide), rzeczpospolita.pl (another Polish daily) - big white area on the right. Also big international news sites don't scale, as BBC, CNN, New York Times (all have white area on the right)
Portals have design very similar to news sites. All well-known Polish portals don't scale: Onet, Wirtualna Polska, o2.pl and Interia. International ones are no better. Yahoo uses approx 60 per cent of the screen. MSN is different, because it has dark blue empty area instead of white. CBS has it black and smaller than the previous ones.
From the sites I have visited, only Google news scales correctly.
It's much easier to find a technical news site that scales. Famous Slashdot scales well, the same with heise.de. Not all look correctly, however: Linux.org has yellow area on the right, Linux.pl - white on both sides.
From Polish FLOSSnews sites 7thguard scales, but Linux news not. New design of hacking.pl doesn't scale, either.
Before checking big companies I throught that those technology-related have websites designed better. And the result: Microsoft, IBM, Intel, NVidia, Dell, HP and Apple have websites that don't scale. The only exception is AMD.
It looks there's much to improve. I'm wondering if the sites are use correct HTML/XML etc. Will probably check it.