Statistics conferences? What are the most significant annual Statistics conferences?
Rules:


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*One conference per answer

*Include a link to the conference 

 A: UseR!

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*List of previous and upcoming R conferences on r-project
Related Links:

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*2011: University of Warwick, Coventry, UK

*Videos of some keynote speakers from 2010
A: In terms of overall breadth, I would say that the ASA/IMS Joint Statistical Meetings are the most significant.  Next year, the statisticians are taking their talents to South Beach...or Miami Beach is more correct.  I just couldn't help to use that line from Lebron James' infamous press conference.  Having said that, I prefer smaller conferences like the UseR! conferences, ICORS (robust statistics), etc.
A: For biostatistics the largest US conferences are the meetings of the local sections of the International Biometrics Society (IBS):

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*ENAR for the Eastern region

*WNAR for the Western region
Of these ENAR is by far larger.
A: Shameless plug: R/Finance which relevant for its intersection of domain-specifics as well as tools, and so far well received by participants of the 2009 and 2010 conference. .
Disclaimer: I am one of the organizers.
A: The main regular conference in Australia is the "Australian Statistics Conference", held every second year. The next one is ASC 2010, to be held in Western Australia in December.
A: This is a new annual conference that should be great for people using statistics and wanting to improve their practical knowledge.  And it will be in warm places in the winter!
The inaugural ASA Conference on Statistical Practice, to be held in Orlando,
Florida, February 16–18, 2012, meets the needs of statistical practitioners
engaged in design, analysis, programming, and consulting. The program for
Statistical Practice 2012 features three main tracks:


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*Research and Development, Engineering, and Operations

*Business Analytics

*Communications, Impact, and Career Development


Both the content and format of this conference have been carefully planned to
improve your effectiveness as a statistical problem solver. Invited sessions,
tutorials, and short courses will refresh your statistical training, update
your knowledge of emerging areas of practice, and sharpen your soft skills.
Poster sessions will give you the opportunity to share and discuss your work.
And if you are looking for employment, a virtual career placement service
will benefit your search.
The timing for this conference could not be better, because the opportunities
for statistical practitioners have never been greater. 
For more information please visit
http://www.amstat.org/meetings/csp/2012/index.cfm
A: Though it hasn't been around for decades, I'm currently looking forward to MCMSki.  One could also mention the Valencia Meetings, but those only happen every four years (and you've already missed the 2010 meeting).
A: Joint Statistical Meetings (JSM) is the biggest meeting I know of. In fact it's almost shocking that after 10 years and as many answers, no one else has offered JSM as a possible "best" conference. But "best" boils down to why you're there.
JSM has 1,000s of statisticians, and many industry sponsors, and top tier keynotes from industry and academic leaders. There's too much to do, from round tables, panel discussions, seminars, workshops, job booths, etc. I never went as a graduate student, but wish I did.
https://www.amstat.org/meetings/joint-statistical-meetings
A: Not a "statistics" conference in the technical sense, but Predictive Analytics World is a case study conference on how companies are using predictive and other analytics in theis businesses.
Predictive Analytics World
A: ACM SIGKDD 2010
KDD 2011 in San Diego
A: These have reasonably a comprehensive list of upcoming statistics events.
Statistics Conferences Worldwide 
IMS meetings calender
Conferences and Meetings on Probability and Statistics
A: This is an upcoming regular conference, that is being held in Sydney, Australia in July 2012, normally the meetings are in Europe: 8th international conference on social science methodology.
The Australian Consortium for Social and Political Research Inc has a conference based in Australia every two years, the one for this year happens to be run combined with the conference I linked above.
A: for statistics in application to educational and psychological measurement, two of the big name north american conferences are the annual meetings for:

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*the national council on measurement in education (hosted in
vancouver, british columbia, canada); and

*the psychometric
society (lincoln, nebraska)

