Here are some of my ideas, which I created by retexturing items to make them in the game.
More Brick Variants
Silver (we have gold already, why not silver as well?)
Silver and Gold Brick Floor
The Cardboard Box that's Been in the Files for Ages
Sapphires, found in Mountain and Forest Mines
Topaz, found in Desert and Tropical Mines
New Wood Flooring
Old Wood Flooring
Reinforced Wood Block
Not Ugly Stone Block
(yes I'm hiding behind a wall for the screenshot, the slyme was trying to murder my face)
What do you think? Have any more suggestions? I will continue to add to this discussion when I come up with new ideas. Comment your suggestions and if they're good, I'll make them and add them to this and credit you.