My favorite is right by the entrance to Grim Batol in the Wetlands. Nice waterfall there and it’s quite scenic.
I hate to say this as a Horde. But Alliance zones have the most beautiful areas. Dun Morogh, Elwynn, Ashenvale. Also IF and SW are just nice places.
In Kalimdor/Eastern Kingdoms: Arathi Highlands.
In Outland: Nagrand.
In Northrend: Grizzly Hills.
Thousand Needles
Ungoro crater