I hope this doesn't seem self serving, but seomoz.org has some of the highest quality information you can find on SEO. In addition to that, I'd suggest articles on http://searchengineland.com/ - they offer high quality content and news in the industry. Anything written by Vanessa Fox on SEL is usually great.

Guides like Excel for SEO shows some of the basic stuff we do: http://www.distilled.net/excel-for-seo/

For high level patent / research based SEO, nobody does it better than http://www.seobythesea.com/ (his URLs are ugly, but his content is great)

For specific beliefs on how the algo works, this is a good resource: http://www.seomoz.org/article/search-ranking-factors

SEOmoz has webinars and a PRO Q&A. Distilled.net also offers videos of our conferences.

As for books, the best I've read are Art of SEO, which is co-written by Rand, and SEO Secrets by Danny Dover (formerly of SEOmoz, now at AT&T) which talks more about the consulting side. The problem with books is that stuff can go out of date quickly. If you're reading a book that talks about PageRank sculpting, for example, it's dated.

Other great sites:

http://www.seobook.com/ - high level opinions and analysis of industry issues

http://www.seroundtable.com/ - recap of industry news and forums

http://www.searchenginejournal.com/ - lots of tactical articles

Things I've written for example:

http://www.distilled.net/blog/seo/how-user-data-may-reorder-...

http://www.distilled.net/blog/seo/breaking-down-the-mormon-s...

http://www.distilled.net/blog/seo/building-your-own-scraper-...

http://www.distilled.net/blog/seo/impact-of-google-instant/

http://www.seomoz.org/blog/replace-yahoo-linkdomain-with-goo...

http://www.seomoz.org/blog/guide-to-competitive-backlink-ana...

Hope that helps! :)