Alcohol Inked Tile Coasters - 25 Decorative DIY Coasters You'll Be Proud to Show off . SourceIf you look at the finished product, you would never guess that these are DIY coasters. All you need are some tiles, rubbing alcohol and alcohol ink!
Use puzzle pieces. Here's How To Easily Make Scrabble Coasters For Your Next Party (instructions don't say to seal the top, but I would just to keep condensation from dripping down in between the tiles and getting icky)