http://bitaverage.com/BTCitAverage takes the last price value from multiple exchange sites (at the moment, 4) and averages it out.
You can view the price of a bitcoin on the home page.
An api is also available in both JSON and XML.
http://bitaverage.com/api?format=jsonhttp://bitaverage.com/api?format=xmlCurrently caching is set to 20 seconds.
To be honest, I was just looking for something to do, so I made this