Quest Announcement/Discussion has multiple pinned resources for quests, but currently Developer's Exchange is left emptyhanded. So I figured I'd post a link to PureZC's Tiles and Tilesets, which currently has the largest selection I know of. :D
All kinds of loose tiles, overworld, interior, sprites, etc. Keep in mind that though all of the various kinds of tilesheets are merged into one section, you can choose what you're looking for and search with the fields above the listing.
Types of tiles: Overworld :: Interior :: Sprite :: Misc.
A wide variety of tilesets available here. Most of them are for 1.92, though.
Types of tilesets: 1.90 :: 1.92
Enjoy, and I hope it's helpful! ;)
This might should be pinned like the other resource topic, but I'll let a moderator decide on that.