Continuing in the tradition of The Tiles Of Xark, the Doodle Tiles are a set of extremely high quality tiles for Hex Kit.
They come with a license to use them in commercial and noncommercial projects, and they cover a pretty broad range of material.
You don't need Xark to use them, and they're fully functional as a standalone, but the art style matches Xark and gives you more options to choose from for any given terrain type.
If you do any kind of hexmapping, the retro hand-drawn aesthetic here is stellar, and I'd strongly recommend checking them out.