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The Google hot topics [webmasterworld.com] thread covers a majority of the topics discussed regarding the algorithm.
"on-page" and "off-page" tend to be the main segregation of factors that affect ranking in all search engines.
The forum index [webmasterworld.com] contains sub-forums dedicated to each of the search engines you've mentioned. There is also a research topics sub-forum that discusses SEO in general as well as a link development forum.
The forum libraries are worth checking out; they contain all the older threads the smart minds of SEO have written about in the past.