stone tiles from home improvement store, add felt to the bottom for inexpensive placemats or hot pads. I like this idea for hot pads, but not so much for placemats.
make your own : stone spa mat I would actually like to make my downstairs bathroom floor out of smooth stones! Wouldn't that be pretty?
Instructions for building a DIY Mid-Century Modern Side Table
Truth be told, my favorite kind of DIYs are the super easy ones that have big impact. Where it looks like you've a complete crafting genius, but deep down, you know you could do it .