Tomorrow, the city and other organizations will mark the sixth anniversary of the September 11 attacks on the World Trade Center. Here's the official city commemoration:

7AM: Families start to arrive at Zuccotti Park, where the ceremony will take place.
8:40AM: Mayor Bloomberg begins the program, which includes first responders reading victims' names and readings from NY Governor Spitzer, former NY Governor Pataki, NJ Governor Corzine and former NYC mayor Giuliani.
Bagpipers and drummers lead WTC Flag to the stage.
Brooklyn Youth Chorus performs Star Spangled Banner.
Mayor Michael R. Bloomberg introduces moment of silence.
8:46AM: First moment of silence, to note when the first plan hit the North Tower. The reading of victims' names begins.
First responders begin reading of names in pairs (118 pairs, 236 readers total).
8:47AM: Families start to descend the Pit at Ground Zero to leave flowers.
9:03AM: Moment of silence to note when the second plane hit the South Tower.
New York Governor Eliot Spitzer delivers reading.
9:59AM: Moment silence to mark when the South Tower fell.
Mayor Rudolph W. Giuliani delivers reading.
10:29AM: Moment of silence to mark when the North Tower fell.
New York Governor George E. Pataki delivers reading. Emily Thomas (flautist) performs Amazing Grace. New Jersey Governor Jon S. Corzine delivers reading.
Program ends when all 2,749 names have been read.
Brooklyn Youth Chorus performs “Bridge Over Troubled Water.” Taps performed by three trumpeters (NYPD, FDNY and PAPD)

The ceremonies will be aired on WABC 7, WCBS 2, WNBC 4, WNYW 5, WWOR 11, and NY1. Church Street will be closed between Battery Place and Barclay, as are Cedar, Cortlandt, Dey, Fulton, Vesey and Barclay Streets between Broadway and Church. And here are some other events around the city:

8AM-3PM: Saint Paul's Chapel offers prayer and civil services.
8:30AM: Ceremonies at the Healing Field, Floyd Bennett Field, Brooklyn.
8:45AM-3PM: Trinity Church has a number of events, including the tolling of change-ringing bells and musical performances.
10AM-5PM: St. Vincent's Hospital Trauma & Wellness Center - A Day of Healing will have a drop-in tent in Battery Park (near the sphere) offering "stress management services to restore calm and provide respite, as we remember that day and continue to move forward, together."
Noon-5PM: Staten Island borough-wide blood drives (PDF).
6PM-9PM: The New York Buddhist Church's Annual 9-11 Memorial Floating Lanterns Ceremony, south side of Pier 40 building at West Houston. "The ancient custom of floating lighted lanterns in waterways symbolizes respect for the lives of people who have gone before us. It also represents a light of hope for peace and harmony that we send over the waters of transmigration." - more information here (PDF).
7PM: "The September Concert: An Evening of Remembrance and Celebration" at St. Patrick's Cathedral.
Sunset: Tribute in Light, the light installation at West and Morris Streets, is turned on at sunset and will remain lit until dawn on Wednesday.
The New-York Historical Society's Here is New York: Remembering 9/11 exhibit opens.

Some additional information:

New plans for Ground Zero were released by World Trade Center leaseholder Larry Silverstein.
Here are the submissions for the WTC Memorial.
September 26, the New-York Historical Society has an event, Reflections on September 11: Lives Lost and Lives Changed, which includes a reading by Don DeLillo and a discussion moderated by historian Kenneth T. Jackson.

Let us know about any other events in comments.

Top photograph of Tribute in Light by imjustsayin in Flickr; bottom photograph of the 9/11 Healing Field at Floyd Bennett Field by GerritsenBeach.net on Flickr