There are a huge number of 4th gen (SNES, Mega Drive/Genesis) games that still look amazing. Some examples that come to mind would be Chrono Trigger, Final Fantasy VI, Super Castlevania IV, Secret of Mana, Super Metroid, and a lot of others.
The 5th generation unfortunately doesn't have quite as many games that still hold up today in terms of visuals. The early implementation of 3D graphics just doesn't look very good. Still, I think there are some games that do still hold up very well regardless, mostly ones that came out late in the generation. Crash Bandicoot 3 is still a pretty good looking game, as is Final Fantasy IX, both on PS1. On the N64 there are some examples as well, like much of Rare's later output on the console, as well as Nintendo's own games naturally.
Once we get to the 7th generation there are just too many games to even list. Developers had gotten used to 3D graphics by this point, and especially later in the generation each console produced some absolutely gorgeous games. On PS2 there were the likes of Okami, God of War 2, Final Fantasy XII, and many others. On Gamecube we had Tales of Symphonia, Star Fox Adventure, Metroid Prime 2, and more. The Xbox also produced a lot of beautiful titles, such as Halo 2, Ninja Gaiden, and Fable.