In this video clip at Centripetal Notion blog, you'll see a neat example of an oscillating chemical reaction:
The Briggs-Rauscher oscillating reaction is one of a small number of known oscillating chemical reactions. It is especially well suited for demonstration purposes because of its visually striking color changes: the freshly prepared colorless solution slowly turns an amber color, suddenly changing to a very dark blue. This slowly fades to colorless and the process repeats, about ten times in the most popular formulation, before ending as a dark blue liquid smelling strongly of iodine.
http://centripetalnotion.com/2008/01/24/13:36:26/ [embedded YouTube]