Subterranean Design. Build a Dungeon from Me. Dungeon Inspiration. All websites that provide ample material to amaze and inspire you. All three of them are fantastic.
A few days ago, I came across 500px, another photo sharing site. Lot's of really nice images there. Then I came across this guy. Wow. Flip through the several pages of his gallery. I guarantee that at least ten of his photos will spark some bit of creativity in your cranium.
Landscapes. Locations for adventures. NPCs. Great stuff.
I want to sit down and write an adventure for at least ten of his photos.