What are some SEO techniques that are considered black hat SEO?

- keyword stuffing (stuffing your webpage with keywords which makes the text looks like it was written for spiders not humans)
- invisible text (using a CSS hidden DIV and/or font color to match the background color).
- buying links could be considered black hat sometime
- cloaking (the content presented to the search engine spider is different to that presented to the user's browser)
- article spinning (rewriting existing articles, or parts of articles, and replacing elements to avoid being penalized in the search engine results pages for using duplicate content)
- doorway pages (a â??fakeâ?? page that the user will never see, but the search engines will)
- subscribing to links farms (is a form of spamming the index of a search engine)

These came in my mind right now...