CastleGarden.org is a database of 10 million passengers to New York, most of whom arrived between 1830 and 1890 (two million more, arriving as early as 1820, have yet to be included). Simple searches for individuals by name and date range are free, and you'll be able to refine your search by specifying occupation, place of origin, and ship. More advanced searches cost $45—however many passengers fit your criteria. Needless to say, this option should be used sparingly, and only if the number of records provided would justify the cost. See this site for information on viewing original manifests.