By me:

The rest is basically my bookmark collection, which hopefully is useful to someone

Doing your own layout:

Accessibility

Finding fonts

Picking colours

Non-PDF options

Help! I want to make a game but art is expensive!

There are three main approaches. First, you can commission art and maps. This is generally expensive. I've written here about the economics of your first product. You can also try to make your own. For maps, Dungeondraft and Inkarnate are good choices, although if making maps doesn't sound fun, maps are usually cheap (see below).

You can also use public domain art. There is a lot online but it can be hard to search. Finally, you can buy stock art. There are a lot of sites for free stock art photos, but usually they aren't fantasy themed. On DriveThruRpg and DM's Guild, you can for a relatively small price buy stock art. Make sure you read the license, though!

You can find some other advice on using low-cost art here.

Free or low-cost maps that allow for commercial use

CZ has also made a lot of map packs with commercial use allowed.
Two minute tabletop allows for LIMITED commercial use, make sure you're adhering to the terms. Large variety of colourful maps.
Kyle Latino (Map Crow) has made some maps that can be used for free, also has some really great map-making tutorials on Youtube if you want to make your own.
Dyson Maps makes a lot of maps available for commercial use. Generally old-school, black and white, including dungeon, town and 3d.

Stock art

Kii has published a few packs of really unique characters.
Vagelio makes some really nice painter-style unique stock art.
Direquest has a lot of templates, layout components, and stock art of items in a pretty cool and distinctive style.
Dean Spenser is a very prolific artist making stock art, including some cover pages.
Daniel Comerci likewise
Tortoise and Hare Creations likewise
Fat Goblin Games seems to publish a variety of different artists' stock art in different styles.
Purple Duck Games likewise.
Castilho makes detailed black and white drawings, including characters, scenes and items.
Feral Indie Studios makes giant collections of spot art for a pretty wide selection of genres.
Perplexing Ruins has a patreon with a lot of art usable for commercial purposes. Great for weird/indie games or just if you want something other than the typical fantasy aesthetic.
StarshineScribbles has created a bunch of creative commons page backgrounds and textures.
Grey Gnome [Free!] has a bunch of black and white stock art that is free for commercial use so long as it is part of a larger commercial project.
Red Ink Caravan has stock art, currently landscapes.
Roselysiumn has a lot of character stock art, and some objects and landscapes.

Public domain art

A Pinterest board of public domain art mostly from the British Library. Maintained by me, I may have made mistakes so double-check before using.
A curated pinboard of more public domain art, themed around "Grim fantasy".
Old Book Illustrations has a good curated list
Artvee for fine art in general.

Misc:

Written Oct 23 2020