Denzi is a pixel artist who has collaborated with Slashing Dragon on Ananias Roguelike (among other things). However, he has also released a fair bit of artwork independent of Slash’s projects, some of which is available at OpenGameArt.

And if I do say so myself, this collection of oblique-perspective, 16×16 pixel tilesets bears a striking resemblance to the art of Ultima 6.

One of many of Denzi’s wonderful pixel art sets. Oblique perspective tiles 16 pixels across. Similar to the old Ultima games. Comes with terrain, monsters, character paper dolls, items, decorations, and more.

You can download the tilesets from OpenGameArt. My only real complaint about them would be the lack of “corner” pieces, which you can see in the screenshots above; there don’t seem to be tiles for e.g. grass corners, resulting in more blocky-looking scenes.