|This picture has nothing to do with the post, I just like it.|
I recently discovered DnD 5E Homebrew on Tumblr and I love it! There's a lot of great stuff, but the Dark Souls conversions are my favorite.
The 5th Edition D&D reddit page has tons of great stuff. StoneStrix monster-of-the-day posts are my favorite. He's compiled many of them into a pdf you can find here.
Tribality has all sorts of fun and useful 5E material. I like their idea of adapting Tyranny of the Dragons and setting it on Krynn. Here is part I and II.
Also, Frog Gods released a free multi-system adventure with their last kickstarter. You can find Rogues in Remballo here.