The New York Times has a map online which can show you population concentrations across the county of various ethnic/national groups from 1880 to 2000. This is an interactive page: you can choose your year of interest and the country of origin you want to focus on...so you can see immigration flows across the country over time. This is a really cool site!
This month's speaker is Bret Rinehart and his topic is immigration laws and a historical overview of them. You can "prep" for his talk by doing some exploring of your own at the Times site. Here is the address: http://www.nytimes.com/interactive/2009/03/10/us/20090310-immigration-explorer.html?hp