Air Canada is offering 1000 miles to new members (who joined Aeroplan between July 1, 2009 and December 31, 2010) who register for this bonus by December 31, book travel by December 31, and fly by March 31, 2011.
If you’ve already taken a flight in the second half of 2010, and were an Aeroplan member at the time, you can still register to earn the bonus.
(Thanks to Henrick.)