The Acadians are one of the more common ethnic groups we think of when anyone mentions Louisiana. Ships records of Acadian travelers are online at http://www.acadian-cajun.com/ship2.htm, along with notes about where they were heading. Not everyone who arrived in New Orleans, stayed in New Orleans.
Creoles migrated from the West Indies. They found friends among the New Orleans Creoles who made them feel a bit more at a home in a new country. The Creole population dates back to about 1720. If you want to research Creole ancestors in New Orleans, you simply must read Creole Families of New Orleans, by Grace Elizabeth King. She gives an extensive history of New Orleans along with the family histories. She also identifies what part of the city Creole families settled.
You'll discover that many of these families had a house in town, in addition to a plantation near the city. Records often note such things as "a large house belonging to M. Chauvin de la Freniere, where he stays when he comes to town (his plantation was above the city)."
Thousands of Germans arrived from the early years and through the 1800s. Mention any place where there was political upheaval or starvation, and you'll find emigrants looking to the United States for a better life. Plus, the emigrant agents were hard at work trying to convince everyone to move to the New World.
The SS Neptune arrived in New Orleans, from Bremen, Germany, in December 1860. Among its passengers were 26 individuals from Frankstadt enroute to Kansas. They appear to represent five families and three single people all traveling together. One person was a carpenter and the rest were farmers.
The ship Italy arrived in New Orleans on May 10, 1852, from Liverpool. On board were 28 Mormons from the Scandinavian Mission with surnames of Dorius, Hansen, Jensen, Knudsen, Olsen, Petersen, Raven, and Schvaneveldt. They were heading to Utah. One might not expect to document Scandinavian Mormons in New Orleans. But there they are on a passenger list proving their place of origin and so on.
There was clearly a Jewish presence in New Orleans prior to the mid-1800s. In 1856, the Jewish Orphans' Home was established - four years before the New York Hebrew Orphan Asylum opened in that city.
An unusual source for research are the reports about the yellow fever outbreaks in New Orleans. In a report by the Sanitation Commission, twenty-one ships arrived in New Orleans from Rio De Janeiro between April 1 and June 28, 1853.
The State of Louisiana web site has a posted passenger manifests online, dating from January 1 through July 7, 1851. The Amistad Research Center at Tulane University is devoted to documenting the history of African Americans and other ethnic groups. They do have a searchable online catalog.
While the Creoles seem to be scattered throughout the city, certain other ethnicities settled in close proximity to one another. Sometimes their names reflect this such as the German Coast where, as you might imagine, German immigrants made their homes. Perhaps the Creoles, French and Spanish felt more at home because of the French and Spanish history of the city, with both languages being spoken throughout. Germans were not a part of the three most common languages spoken: French, Spanish, and English. By establishing a German area, they could more easily retain some of their own ethnicity.
New Orleans has been amazingly cosmopolitan in terms of the myriad of ethnicities setting foot in her ports. Some ethnic groups retain a significant presence today while others were merely passing through.