I might as well chip in with some unused graphics I found in Ultima VII and Serpent Isle while going through the game resources via
Exult.
There are frames for a flying gargoyle which is not used anywhere in the game.
Several of these business signs are not used in the game. Some, like the key for guild shop and ankh for healer stem from earlier games in the series. The three red globes was possibly meant for pawn shops, as in the released game you can sell only a couple of very specific items. The red bull sign is from Serpent Isle, and used in place of the horse sign.
Some of the characters have frames for special actions which are not used in the game. On magic-able characters these frames are used for spellcasting gestures.
Then there's this thing. It's labeled as "prism" in the game files. I have no idea what it might have been intended for. The colors are actually transparencies which make whatever is behind it lighter. This is how it looks on a black background.
This is a bunch of important quest item graphics that are grouped together in the Serpent Isle files. The third one is labeled "the cat's eye", and is not used in the game. This is probably related to a cut section of the game called Cat Isle. The one in the middle is a small gong, which I do not remember being used anywhere in the game either.
Finally, here are paperdoll graphics for a cloak which is not in the game. The glowing edges would animate in the game, streaking around the cloak.
edit: Sorry I wasn't able to figure out how to display the images in full size in the post itself.