Crucible of Realms

Instead of a book or game, promoting on of my favorite podcasts of all time: Crucible of Realms

http://www.crucibleofrealms.com/

These guys did an amazing job creating random worlds as hosted by Jim "the awesome" Ryan, one of the most creatively insane minds of our generation.

http://jimyesthatjim.com/

Let them know how awesome they are. :)

5e Homebrew

https://github.com/gguillotte/mdsrd5/

I haven't had a chance to look too deeply, but it was recommended highly by a friend of mine.

best I can tell, it tries to fill in a lot of holes.