The New York Times has a great tool on their Website that gives insight into US immigration patterns:

http://www.nytimes.com/interactive/2009/03/10/us/20090310-immigration-explorer.html?ref=us

It's interactive, you can select country/region of origin, and you can look at actual size of the population as well as percentage. Anybody interested in researching and targeting ethnic audiences should check this out! Compliments to Matthew Bloch and Robert Gebeloff of the NYT for putting this together.

Immigration-Explorer-NY-Tim