Where should I report sites that have obvious signs of black hat abuse?

Question

I have found several sites that are using black hat techniques to rank higher in search results. Where can I report those sites.

Answer 1

The quality guidelines section of the Google Webmaster Guidelines contains this link for submitting sites which use blackhat/spammy practices. I believe the feedback page on Google search results also has a link to the same form.

Edit:

Google has also released a Chrome extension to easily report spam sites. It provides a browser button that'll take you directly to the spam site submission form and autocomplete certain fields.

There is also a similar plugin for Firefox.