I found these on the GreenHead.com site and thought they were so neat!  These are glass plant waterers that are shaped like a stone.  You fill the glass stone with water and put it on top of the soil in one of your potted plants.  It slowly releases water over 3 to 4 days.  The water seeps out through a tiny release hole. 

This is a great solution if you have to be away for a few days and want a reliable way to water your potted plants and flowers.  Designed by Casey Schneider.