Amethyst Ore
Amethysts can be found, rarely between levels 25 and 0, deep underground. You can make some awesome stuff with this purple beauty!
Salt Ore
Salt ore kill ants. Great for keeping ants out of places you don't want them! Place a few Salt ore in front of your door. Double wide does the trick. Sometimes ants will cross just one block. Or you can smelt this to make some salt for your popcorn! Yum!