Here is a rather large map showing the nationalities of the inhabitants of Reykjavik. Each dot represents around 25 people. You can click on it for higher defintion. 
The Icelanders are shown in gray, since they would otherwise dominate the map. The locations within each district are representative only, so do not expect to meet 25 Lithuanians at an exact location of a green dot. There are some interesting patterns to be see here. The most diverse districts are the City centre, Vesturbær, Austurbær and Breiðholt. Breiðholt is particularly popular among Poles and Lithuanians whereas those from Westernern Europe and the USA prefer the city centre. This one is inspired on New York Times’ visualization of the US-census, called Mapping America, Every City, Every Block. I got the data for the most populous nationalities in every district of Reykjavik from the Statistical Office of Iceland. You can see the file I ended up using here: distvsnat.xlsx.