The following are AD&D resources that I value. You may not. Let me know in the comments if you have something better.

AD&D Toolkit Discord

It’s free to use! Our discord community connects DMs and Players to form campaigns, share information, sell/trade collectibles and materials, as well as offer support for the AD&D Toolkit. Basically, it is your one-stop shop for everything AD&D 1e.

DriveThru RPG

DriveThru RPG is a great resource for D&D manuals. They sell hard cover reprints as well as downloadable PDFs for $10.

TableTop Audio

It’s free to use! TableTop Audio(https://tabletopaudio.com/) is a third-party site that offers a large number of audio files for DMs to use in their game sessions. There are all sorts of genres. There is both music and simple ambience, like forest sounds without music overlay. The interface is slick and renders well across browsers. Works well on mobile. Just a top-notch job. It’s even partnered with roll20.net for integrated sound DMs can share with their players virtually through the VTT.

Roll20

It’s free to use! Roll20(https://roll20.net/) is a Virtual Table-Top(VTT) that offers a large part of its application for free. There is of course a subscription plan that affords some extra perks but the bulk of it is available on the free version. This includes integrated chat, TableTop Audio sound management, a die roll system, character tokens, importable images, Fog of War on your maps, all for free. It is not without criticism however. I find it to be quite buggy. It does not work well in some browsers. It does not work well on mobile devices. On older ones it evens breaks. The interface is quite cumbersome.

Dungeon Scrawl

It’s free to use! Dungeon Scrawl boasts the ability to easily create and customize dungeons and battlemaps for any tabletop RPG or adventure – No downloads or sign-up required. Export for virtual tabletops or print for your next game night.