The date of the attack: 9/11 - 9+1+1 = 11
September 11th is the 254th day of the year: 2+5+4 = 11
After September 11th there are 111 days left to the end of the year.
119 is the area code Iraq/Iran. 1+1+9 = 11
Twin Towers - standing side by side, looks like the number 11
The first plane to hit the towers was Flight 11

WAIT THERE IS MORE...

State of New York - The 11 State added to the Union
New York City - 11 Letters
Afghanistan - 11 Letters
The Pentagon - 11 Letters
Ramzi Yousef - 11 Letters (convicted or orchestrating the attack of
the WTC in 1993)
Flight 11 - 92 on board - 9+2 = 11
Flight 77 - 65 on board - 6+5 = 11