A collection of information and tools for search engine optimisation, or search engine marketers.
A solid set of guides is available as well as tips coming straight from authoritative sources, like Google itself, including the one and only Matt Cutts.
Research how your site is doing with backlink research tools and SEO analysis tools. WooRank stands out in particular in providing a wealth of information that'll help you optimise your site for search engines.
SEO is often a misinformation minefield, so try to keep things cited and appropriate - oh, and don't spam your own high keyword density outsourced articles. :)
Feel free to add more as you find them.