Implement something similar to a captcha: Ask questions only people from your neighborhood can answer. Make sure the answers are not too easily found by using google.

It does show that I'm at slashdut.com, and as I don't want to be there, I'll leave that site and head for slashdot.org, instead.

Of course, I could miss that little difference in the domain names. But that's not solved by high-security-certificates, either, as slashdut.com may actually be registered by a corrupt company with that name and may have bought a matching high-security-certificate.

Together with my 'lock current key to current site'-idea, this could be solved by making the browser bar green only if I'm currently surfing a website using a key which I have approved myself in the past. This would be a much better indicator of a valid site than a certificate by some random company.