Immigrant Ships Transcribers Guild
http://www.immigrantships.net/
Transcriptions of passenger lists done by volunteers. Also has ship descriptions, etc.
The Olive Tree Genealogy
http://olivetreegenealogy.com/index.shtml
Includes ship passenger lists, info on Palatines, New Netherlands (NY) genealogy, and more. All free
Palmer List of Merchant Vessels
http://www.geocities.com/mppraetorius/
CastleGarden.org
http://www.castlegarden.org/index.html
Free access to a database of information on 10 million immigrants from 1830 through 1892 who arrived in NY.
The Statue of Liberty-Ellis Island Foundation
http://www.ellisislandrecords.org/
This database provides access to passenger arrival records of about 22 million people whose names appear in the original ship passenger manifests for the Port of New York from 1892-1924.