With the exception of Ancestry.com and Find My Past all of these websites are free. Some of them require registration.
https://www.archives.gov/ (National Archives)
https://chroniclingamerica.loc.gov/ (Library of Congress)
https://www.cruisedirect.com/finding-your-family-from-ship-passenger-lists "Finding Your Family from Ship's Passenger Lists" (Contributed by Addison and John Moyer)
https://www.gaylord.com/ (preserving family history)
https://www.libertyellisfoundation.org/ (Statue of Liberty – Ellis Island)
http://home.rootsweb.ancestry.com/ (available through Ancestry.com; however currently unavailable)