Panda 4.1 (#27) — September 23, 2014
Google announced a significant Panda update, which included an algorithmic component. They estimated the impact at 3-5% of queries affected. Given the "slow rollout," the exact timing was unclear.
Authorship Removed — August 28, 2014
Following up on the June 28th drop of authorship photos, Google announced that they would be completely removing authorship markup (and would no longer process it). By the next morning, authorship bylines had disappeared from all SERPs.
HTTPS/SSL Update — August 6, 2014
After months of speculation, Google announced that they would be giving preference to secure sites, and that adding encryption would provide a "lightweight" rankings boost. They stressed that this boost would start out small, but implied it might increase if the changed proved to be positive.
Pigeon — July 24, 2014
Google shook the local SEO world with an update that dramatically altered some local results and modified how they handle and interpret location cues. Google claimed that Pigeon created closer ties between the local algorithm and core algorithm(s).
Authorship Photo Drop — June 28, 2014
John Mueller made a surprise announcement (on June 25th) that Google would be dropping all authorship photos from SERPs (after heavily promoting authorship as a connection to Google+). The drop was complete around June 28th.
Payday Loan 3.0 — June 12, 2014
Less than a month after the Payday Loan 2.0 anti-spam update, Google launched another major iteration. Official statements suggested that 2.0 targeted specific sites, while 3.0 targeted spammy queries.
Panda 4.0 (#26) — May 19, 2014
Google confirmed a major Panda update that likely included both an algorithm update and a data refresh. Officially, about 7.5% of English-language queries were affected. While Matt Cutts said it began
Payday Loan 2.0 — May 16, 2014
Just prior to Panda 4.0, Google updated it's "payday loan" algorithm, which targets especially spammy queries. The exact date of the roll-out was unclear (Google said "this past weekend" on 5/20), and the back-to-back updates made the details difficult to sort out.
Unnamed Update — March 24, 2014
Major algorithm flux trackers and webmaster chatter spiked around 3/24-3/25, and some speculated that the new, "softer" Panda update had arrived. Many sites reported ranking changes, but this update was never confirmed by Google.
Page Layout #3 — February 6, 2014
Google "refreshed" their page layout algorithm, also known as "top heavy". Originally launched in January 2012, the page layout algorithm penalizes sites with too many ads above the fold.