Open Access Week 2011 will take place all over the world between October 24 and 30. In future, Open Access Week will be the last *full* week of October:
2011: Oct 24 - 30
2012: Oct 22 - 28
2013: Oct 21 - 27
2014: Oct 20 - 26
2015: Oct 19 - 25
Further information under http://www.openaccessweek.org/