This can be extended to promotional art too. The one that immediately jumps out in my mind is Final Fantasy Tactics Advance because of the absolutely stunning color contrast it has going on. Doom’s is also just iconic. Lots of really great art out there and I’d love to hear others’ opinions on their favorites!
For the purposes of this community, “retro” means platforms launched in 2001 and earlier, and games for those platforms released through roughly 2007. This means that the Xbox, GameCube, Game Boy Advance, and PlayStation 2 are the cutoff consoles.