National Map

http://www.ling.upenn.edu/phono_atlas/NationalMap/NationalMap.html

Website designed by the University of Pennsylvania. It contains an overall view of the Telsur project which focuses on the analysis of the vowel phonological systems of urban dialects in the US and aims at creating a Phonological Atlas of North America. The results of the first phase of the project are based on the acoustic analysis of 240 Telsur interviews carried out so far, with further data from a broader analysis of the full sample of 640 speakers representing urban areas.
According to phonological criteria, the project defines 4 large dialectal regions (the North, the West, the South, and the Midland) and calls attention to a change that has taken place in the dialectal boundaries of the US since 1987. Various charts and maps are provided showing the distribution of defining linguistic features of each region. The initial evidences gathered by the project point to an intensification of the great regional phonological patterns rather than the development of specific urban dialects.
The website is heavily descriptive and technical, but no recorded samples are provided for the dialects in question.