In the interests of sharing the love -- recommend a D&D resource you think is awesome, but which maybe not everybody has heard of. Maybe it's a book, a blog, a web page, an accessory, an electronic tool, a prop - if you use it in/for your D&D game, let us know what's awesome about it. Try to keep to things you have no involvement with though!
So, what awesome D&D resource do you think more folks should use?
Adventures in Middle Earth is excellent for actual 5e material. I also love the old ICE MERP (Middle Earth Roleplaying) materials for their presentation design and maps. For example, Moria is absolutely enormous, rather than the 60-room dwarven "cities" and such that have been published for D&D.
I'm a fan of more "realistic" maps and such, so the Theban Mapping Project:
http://www.thebanmappingproject.com is a big one for tombs.
Google search for actual maps for caverns and caves, they are far more interesting than most published maps.
Older D&D materials in general, but AD&D era releases, including Dragon magazine, have a lot of interesting approaches and perspectives. In addition to being an era where there were more articles attempting to simulate realism with rules (some of them insanely complex), but you get a better understanding of the evolution of many things in the game which can help with adjudication and tweaks.
OD&D/1e era 3rd-party releases such as Bard Games, Judges Guild, Palladium, Role Aids (really...), and others are great because they often had wildly different approaches (and quality), than TSR did.
Although well known, the original Volo's Guides are among my favorites, and get constant use. Not just for their content, but because I greatly prefer releases with more fluff and flavor than crunch. I have the rules, I'm always looking for ideas and inspiration.
