http://searchenginewatch.com/searchday/article.php/3483601
Sixteen flavors of search engine spam is an excerpt from an article at above URL.
A comprehensive list of sixteen tactics that are considered search engine spam. These techniques include:
Keywords unrelated to site
Redirects
Keyword stuffing
Mirror/duplicate content
Tiny Text
Doorway pages
Link Farms
Cloaking
Keyword stacking
Gibberish
Hidden text
Domain Spam
Hidden links
Mini/micro-sites
Page Swapping (bait &switch)
Typo spam and cyber squatting