Economic impact of September 11, 2001 terrorist attack

http://en.wikipedia.org/wiki/Economic_effects_arising_from_the_September_11_attacks

Recessions:

http://www.calculatedriskblog.com/2012/10/real-gdp-increased-20-annual-rate-in-q3.html
http://en.wikipedia.org/wiki/List_of_recessions_in_the_United_States