The British Library has an awesome map of regional dialects of the UK (http://www.bl.uk/learning/langlit/sounds/index.html), though the timespan is rather limited (only about 100 years in terms of birth dates of speakers). It's pretty extensive, with each dialect getting a 5-10 minute recording and a few paragraphs on its notable linguistic characteristics. Great time waster!

This is more contemporary, but here's a massive database of dialect recordings: http://accent.gmu.edu/browse_language.php