The NARA website has added the below, searchable passenger lists their site:
http://aad.archives.gov/aad/series-list.jsp?cat=GP44

These passenger lists cover:
Immigration of Russians to the United States, 1834 - 1897
Irish Famine, 1/12/1846 -12/31/1851
Germans to the United States, 1850 - 1897
Italians to the United States, 1855 - 1900