Shower Timers are exactly that timers that can go with you in the shower to keep your time down in order to save water. According to the Shower Minder website an average family of four can save up to $400 a year by using Showermanager. It just seems like a rather simple water saving concept.
Check these fun shower timer designs in Zwello...
http://www.zwello.com/bath.html
But then it gets better for conservation with the Shower Minder
http://www.showermanager.com/index.shtml