What are the specific, key metrics you track on an ongoing basis for your sites' SEO health?

I'll start with a few of mine (not exhaustive by any means):

Traffic
-- # of visits from each search engine
-- # of pages receiving visits from each search engine
-- # of keywords sending traffic from each engine

Links
-- # of linking root domains (from GWMT and Linkscape/OSE)
-- # of sites sending referral traffic
-- Domain Authority, Domain mozRank, Domain mozTrust

Content
-- Number of unique pages of content (by section/type)
-- Top content by linking root domains, # of search visits and # of referring keywords

Rankings
-- Rank position for all high volume, head terms
-- Rank position for a sample set of chunky middle and long tail terms
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