You should check out the really good list at – Search Engine Ranking Factors | SEOmoz
But if I was to add to your list based on my own observations and SEO experience, i’d say regular content updates are very important for rankings.
I recently updated a few of my sites that haven’t been updated for a long time, and they started ranking better in Google a few days later. Search engines don’t like stale websites, its a sign that they are not active and no longer relevant possibly.