Cimorelli.com
Ships arriving US from Europe (Morton Allan Directory)

Ellis Island
Ellis Island Passenger Lists records for most of the 25 million immigrants who arrived there from 1892 to 1924. Most easily searchable through Steve Morse.

Immigrant Ships Transcribers Guild
Passenger lists.

Stephen Morse
Steve Morse’s One-Step website started out as an aid for finding passengers more effectively in the Ellis Island database. Shortly afterward, he expanded his tools to improve searching the 1930 census. His site has continued to evolve and today includes over 100 web-based tools divided into 12 separate categories, ranging from genealogical searches to astronomical calculations to last-minute bidding on eBay.