Easily GTA4 still. While some others are better looking....Im more impressed with a living, breathing busy city thn settings that are far less "alive" populated, dense, barren etc. GTA4 is just huge and every inch of it is packed, you cant say the same or on the level n scope of a open world city thn GTA4.
FUEL also impressed me on a technical level...graphics may not be amazing but you can take every single games world mentioned in this topic, combine thm and still not as big of a world as FUEL has. Very impressive and holds record for largest gaming world that doesnt randomly generate anything at all.
Real Hip Hop...I miss the 90's http://www.youtube.com/watch?v=Q8ua89wKwDA&feature=related
Easily Red Dead Redemption.. especially the 360 version (I have and play both). The landscapes in that game are just gorgeous. Not many games actually have wowed me as much as RDR has. I easily find myself getting lost in the beauty of that game quite bit whenever I play it.
The Assassin's Creed games are up there too. All of them have looked damn good and I don't think they get enough credit for their visuals.