I personally find the crashed battleship in Mor Dhona and sight of Ishgard in Coerthas both pretty breath-taking. But those are particularly obvious.
A rather unknown place that I also greatly like it's the ceruleum mine in Thanalan, it's a huge hole in the ground with many smaller refineries dotting around it. It's like a huge quarry.

It's sad because most of the best scenery in the game is tucked away where nobody has any reason to go to, but you'll get to see most if not all of them by acquiring the Wanderer's Shadow achievement. I suggest you give it a go!