http://www.dnscoop.com/
A very interesting website. It attempts to estimate a value for an established website or a domain name by using factors such as:
    * Links pointing to the domain
    * Popularity of the domain
    * Age of the domain
    * Pagerank of the domain
    * Traffic to the domain
    * and more...

I quickly tried rookiesite.com. $150. Ok, it's expected. Actually not too bad.
Then, "The estimated value of http://dnscoop.com is: $102,820."
Lastly, I entered the No. 1 site in the world: Yahoo.
"The estimated value of http://yahoo.com is: $1,884,000,000"
Hmm, this is much less than $47.5 billion offered by Microsoft. Seeing such as a great offer vanish, no wonder Yahoo's shareholders are very very mad...
Apparently this site provides very fun information.