How Much Is Your Blog or Website Worth?
I was reading through my daily newsfeeds and came across a blog post by Calvin Cox at StyleApple entitled How Much Is Your Website or Blog Really Worth? Calvin discovered a website called CubeStat that does an automated valuation of your website, include an estimate of potential ad revenue.
You may not be able to take that valuation to the bank, but it still gives you a good ballpark as to whether your site is living up to its income potential. Or if you have a personal site or blog that you're not earning money from yet, it will give you an idea what you could be earning.
One caveat I discovered -- it doesn't recognize subdomains properly. I put in http://entrepreneurs.about.com as a test, and it told me the site was worth $28 million and capable of generating $38,824 a day in ad revenue. Clearly those numbers are for all of About.com, not just my subdomain (and no, I have no idea how accurate they are, so don't ask!). Still, the valuation methodology does have some basis in reality and is a worthwhile exercise (be patient -- it takes a minute or two, literally).
Related on About.com:

Comments
WebsiteFact is a good tool. It gives semi reasonable calculations based on some good data
It truly amazes me how many websites there are that say what a website is worth. One website I’ve been to before says $57, the next says $1,300, another about $4k. I’m sure its probably somewhere in the middle. Worth is probably based on both revenue as well as unique hits. BTW, I like cubestat the best I think (of all of em). Cheers, Kerry