Real-time Search - December 2009
This time, real-time search was for real- Twitter feeds, Google News, newly indexed content, and a number of other sources were integrated into a real-time feed on some SERPs. Sources continued to expand over time, including social media.
Caffeine (Preview) - August 2009
Google released a preview of a massive infrastructure change, designed to speed crawling, expand the index, and integrate indexation and ranking in nearly real-time. The timeline spanned months, with the final rollout starting in the US in early 2010 and lasting until the summer.
Rel-canonical Tag - February 2009
Google, Microsoft, and Yahoo jointly announced support for the Canonical Tag, allowing webmasters to send canonicalization signals to search bots without impacting human visitors.
Learn about the Canonical Link Element in 5 minutes (MattCutts.com)
Vince - February 2009
SEOs reported a major update that seemed to strongly favor big brands. Matt Cutts called VInce a "minor change", but others felt it had profound, long-term implications.
Big Brands - Google Brand Promotion: New Search Engine Rankings Place Heavy Emphasis on Branding (SEO Book)