Laura has a good posting about learning Spanish and the dialect used around Buenos Aires. It reminded me about a project at the University of Iowa, Phonetics: The Sounds of English, German, and Spanish. If you have problems figuring out exactly where to put your tongue when trying to speak any of these languages, the Phonetics site has some very good instructions, complete with a flash-based diagram and online audio and video of a person speaking the sound.
I was impressed that the site not only has the rioplatense dialect but also the caribeño. In Miami I had a much more difficult time understanding Cuban speakers. The University of Iowa site showed why.
The Iowa site is good for those also learning American English, though I don’t think that they got all those ancient Southern diphtongs that we use back in Tennessee!
There are now quite a number of audio resources on the net now for learning different accents and dialects. I’ll try to post some more links as I come across them.