This is a cool touch sensor from DFRobot. You can hook it up to the IO Expansion shield (for arduino) directly. It includes a metallic tape with a sticky side. This make it possible for you to place your sensors anywhere you want. So, if you get sick of the typical push buttons, try this invisible button for your projects! This touch sensor works on a variety of surfaces; Metal, glass, plastic, rubber. It does not work on cardboard or wood.
 

NOTE:This sensor requires some basic soldering.