We have American houseguests at the moment, so not a lot of time to blog, but lots of time to sit around and listen to other Americans' impressions of BrE. So far, we've discussed pudding/dessert, Jell-o/jelly (both mentioned back here) and something else that we discussed for at least a few minutes and that I have now forgotten completely.
So, in the absence of time/presence of mind to write much more, here are some recommendations for resources on regional accents. The British Library has recently unveiled their Sounds Familiar? website. This is a wonderful resource, full of descriptions and recordings of various dialects in the UK.
Looking for something somewhat similar for the US, I found the Varieties of English website at University of Arizona. This covers other Englishes in addition to American--and doesn't cover the whole of America. (For instance, the English of white Arizonans isn't treated at all.) But if you click on 'Southern States' or 'Northeast US', you get some general description and sound samples. A classic (meaning that it already existed when I started teaching) American dialect 'edutainment' is the film American Tongues. If you can find a copy, it's definitely a good one.
If you have other dialect audio-visual resources to recommend, please do so!