Splinter Cell CT and Chronicles of Riddick.
IMO, nothing else comes remotely close.
I know a lot of you are mentioning Doom 3, but the xbox version was soo drastically downgraded from the PC that it's hard for me to include it.
Splinter cell 3 and Riddick looks better on PC too, xbox version is pretty much low settings equivalent. Splinter cell 3 on PC has shader model 3 features, higher resolution shadows and much improved textures, the same with Riddick. Doom 3 on xbox has a little bit rebuilded levels, but other than that compromises are similar like in these two games (what's more doom 3 has no dynamic resolution scaling unlike Riddick)
Can you guess during first second witch screenshot is xbox version and witch is PC maxed out? Personally I cant, I have to look for subtle details in order to tell a difference and that's how doom 3 on xbox looks for the most part. IMO Doom 3 on xbox was very good port and it looked even better on CRT, becsuse on CRT low quality textures and low poly objects imperfections are masked very well, while on PC low poly objects and textures just hits you in the face.
And here's Splinter Cell 3 PS2 vs Xbox, I can tell a difference immediately without looking for suble details. According to you doom 3 looks drastically different on xbox, so what word you will use to describe difference between PS2 and xbox port of splinter cell 3?