Various dialect maps of English (and other languages) are available on the internet. IDEA (International Dialects of English Archive) provides samples of recordings of English dialects and accents from around the world. Although intended for use as models for actors, the recordings are worth listening to.
Wikipedia provides information on some of the basic features of a number of dialects of English spoken in a number of countries, as does this link. For a good information on dialects of English in the USA and a map, see A National Map of The Regional Dialects of American English, by William Labov, Sharon Ash and Charles Boberg
A fantastic resource is the Kindle edition of Atlas of North American English. Book and CD-ROM. Phonetics, Phonology and Sound Change by the same authors, available for free on Amazon
[All links were operational when accessed May 2016]
