D&D Resources
D&D 5e is a massive system and having the fun base mainly on the players allows for a massive amount of expansion and creativity, therefore, having a massive collection of resources in one place may help.
I will be organizing this into categories of Dungeon Mastery, Maps, Music, Game Supplements, and Other
and of course, the essential resource, the Player's Handbook http://orc-news.ru/dnd5eng.pdf
This page is still WIP
Dungeon Mastery
The Complete Hippo
A massive resource for improving your campaigns.
https://www.reddit.com/r/DnDBehindTheScreen/comments/agf4k7/the_complete_hippo_2019_update/
The Dungeon Master's Guide
The official supplement from the owners, it may help you with coming up with your campaigns and such.
Player's Basic Rules Guide
A compressed version of the rules for D&D, it's still a hefty read, but it's easier to get the information.
https://media.wizards.com/2014/downloads/dnd/PlayerDnDBasicRules_v0.2.pdf
r/DnDBehindTheScreen
A bunch of people sharing Resources and stuff like that
https://www.reddit.com/r/DnDBehindTheScreen/
D&D Wiki
Provides compressed rules and homebrew articles for 3.5, 4, and 5th edition
https://www.dandwiki.com/wiki/Main_Page
r/DMAcademy
It provides a similar role to r/DnDBehindTheScreen
https://www.reddit.com/r/DMAcademy/
Game Supplements
Unearthed Arcana
This isn't an official version, nor am I sure if it's completely 5e, but UA adds some interesting features, including the Artificer.
https://minisgallery.com/uac.pdf
Xanathar's Guide to Everything
Adds some DM tips, namelists, and some character options.
The Monster Manual
Pretty much one of your best resources in selection and or creation of monsters and other encounters
http://orkerhulen.dk/onewebmedia/Monster%20Manual.pdf
Arcane Artillery
Guns, Guns, Guns!
https://drive.google.com/file/d/0BwRBp4t9A8LbM0ZDdkRObHdzX0E/view
Maps
Dungeon Painter Studio
My main resource to make maps, a little buggy, but it's easy to learn. You will have to pay for it.
https://store.steampowered.com/app/592260/Dungeon_Painter_Studio/
r/DnDMaps
A subreddit where people share maps
https://www.reddit.com/r/dndmaps/
Google Images
I mean, come on, you can find something there.
Music
Ah, music, the mathematical arrangement of sound. Proper selection can make an ancounter, and can allow for proper roleplay.
I'm going to place this music into themes, but use them as you wish.
Ambience
Combat
Tussle in the Tavern
https://www.youtube.com/watch?v=UY6JduQlMRQ - Assassin's Creed 3, Fight Club (10 min)
https://www.youtube.com/watch?v=_nhl0XswsfA - Dragon Age Origins, Tavern Brawl (1 min)
https://www.youtube.com/watch?v=uTnB-Wn0b0Q - Divinity Original Sin 2, Tavern Fight (3 min)
https://www.youtube.com/watch?v=-Q5Y037vIyc - The Drunken Gambler, (2 min)
https://www.youtube.com/watch?v=PN7EkJv98PQ - Pirates of the Caribbean, Two Hornpipes (6 min)
https://www.youtube.com/watch?v=SBATrLRWySg - Irish Tavern Music (11.5 min)
Battle Against Brigands (and other folk)
https://www.youtube.com/watch?v=P8BAgLNPpDI - Witcher 3, Go For It (15 min)
https://www.youtube.com/watch?v=nugiDjvyf-4 - Witcher 3, Ard Skellig General (4.5 min)
https://www.youtube.com/watch?v=QjeY7SrbLgk - Immersive Music Suite (1.5 hr)
https://www.youtube.com/watch?v=E7JzX4CHJYg - Darkest Dungeon, All Things Must Come (3.5 min)
Holding Back the Horrors
https://www.youtube.com/watch?v=CsW72KIOd8U - Darkest Dungeon, The Final Combat (5 min)
https://www.youtube.com/watch?v=o_YXZxBfIyM - Darkest Dungeon, Bloodletting of the Crimson Court (6 min)
https://www.youtube.com/watch?v=Ma-WJUidpRU - Darkest Dungeon, Town in Chaos (6.5 min)
https://www.youtube.com/watch?v=BKWtwJ38EjE - Witcher 3, You're... Immortal (11 min)
Encounter in Elysee
https://www.youtube.com/watch?v=2qQMXDvZRY4 - AC Unity, Fight Theme (1.5 min)
https://www.youtube.com/watch?v=yyevCjnjRg4 - AC Unity, Chase Theme 1 (1.5 min)
https://www.youtube.com/watch?v=T1nY3hLEM00 - Witcher 3, Wine Wars (15 min)
Reddit Postings
https://www.reddit.com/r/DnD/comments/595zc6/my_curated_spotify_playlists_i_use_for_dd/ - Some dude curated a bunch of these and seems to have taken from a variety of sources
https://www.reddit.com/r/DnDPlaylist/ - Turns out there's a whole subreddit for this too.