I have come across a tool which tells you based on Alexa as well as other rankings your sites approx. value. Well I believe the actual value part is not accurate as it does not take many other factors into consideration. However I do believe the actual visitor traffic numbers and inbound links are quite important. Also the google adsense earnings are close to the actual figures.

Try it for yourself by visiting Website value calculator and web information

Let me know your thoughts here.