“There’s a plane in the Hudson. I’m on the ferry going to pick up  the people. Crazy.”
Janis Krums was the first person to offer an image and a commentary of the incident, through TwitPic.

Update: Some great compilations of various reports from kottke.org ‘Hudson River plane crash’, including a terrifying video of a similar incident, and in Flickr. On other media:

On the press:
EL PAIS: A salvo los 153 ocupantes de un avión que cayó en el rio Hudson de Nueva York 
LA TIMES: All safe after US Airways jet goes down in New York’s Hudson River
The Guardian: Plane crashes in Hudson river in New York
There is more in Google if you care to search.
And guess what, Once again, Twitter proves its worth as it happened with the Mumbai terror attacks

That is the real NEW in this event: Twitter is worth. It is an incredible tool for communicating as it happens.
You just can not be a photographer, a journalist, an academic, or just a citizen, and not know about Twitter.