"Adults can acheive a native-like accent in Japanese. Japanese TV showcases foreigners (like "Amazing Pets") who speak Japanese quite frequently."
Wow, you really watched TV in Japan!! The so called "tarento" (From English "Talent" foreigners are considered like that just because they are Japanese-speaking Pets so I would REFUSE to appear on TV just so that people laugh at my Japanese (actually people stopped laughing when I learned Osaka-ben ;)
I don't know the book that K.T. suggested but I believe that "Aural Comprehension in Japanese" is an excellent book for a student who wants to SOUND LIKE A JAPANESE and speak convincingly in Standard Japanese. Too bad I came to Osaka and forgot everything I learned with this book...
"If you learn Japanese, I recommend that you learn the standard Tokyo accent. This is usually what is taught by teachers-but not ALWAYS!"
This is a very good advice!!! Unless you can learn a local language WELL and, most importantly, switch back to STANDARD JAPANESE whenever necessary I wouldn't suggest trying to learn dialects because that will rule out any possibility of getting a job for using Japanese.
"If you plan to come to Japan and live in Osaka, you should ask J.C. here about Osaka-ben (the Osaka dialect). Another dialect is the Kyoto dialect."
Osakaben is the only thing I speak now :)
There are some good books for studying it:
Colloquial Kansai Japanese:
http://www.amazon.com/Colloquial-Kansai-Japanese-Dialects-Language/dp/0804837236
Kansai Japanese:
http://www.amazon.com/Kansai-Japanese-Language-Osaka-Western/dp/0804818681/ref=pd_sim_b_12
They are a good introduction to understand Kansai Japanese but deal rather with an older and more traditional Kansai Japanese. It's a little different from what young people study. But only learn it if you intend to live in Kansai. It's considered rude by people from other regions (I don't care!!!). It's like someone from New York talking in California...
"Tokyo=standard (good for men and women)
Osaka=said to be a manly dialect
Kyoto=said to be a feminine-sounding dialect"
Other than Standard Japanese I would learn either Osakaben or Kyotoben because these dialects are understood throughout Japan.
"J.C. knows more about regional accents that I do. People in Hokkaido seem to speak standard Japanese."
During my graduate studies I had the opportunity to partake in dialect research and helped describing dialects in Kyushu (Nagasaki and Kumamoto), Tokushima (Close to Kansai dialect) and Akita (Northeast dialect). Because of that I studied a little about the grammar and phonology of these dialects, which helped me improve the understanding of most dialects spoken in Japan (Okinawa has a different group of dialects from which I studied the language spoken in Shuri, former capital of the Ryukyu kingdom). However, I have no idea of what people are talking about when I hear Tsugaru-ben (津軽弁), spoken in Aomori and kagoshima-ben (鹿児島弁) from Kagoshima prefecture. The interesting thing is that Tsugaru-ben is spoken in the Northeast (tohoku) part of Japan but it totally different from the adjacent dialects. The same can be said about Kagoshima-ben since Kagoshima is located in Kyushu but doesn't sound like Kyushu dialects.
When I went to Hokkaido in 2000 I felt the language is totally different from Tohoku and quite standard. But I believe they have some tohoku-ben influence as far as vocabulary is concerned.
I found some interesting examples of tsugaru-ben and kagoshima-ben:
tsugaru-ben:
http://www.youtube.com/watch?v=89NkrQnD7ZI
kagoshima-ben:
http://www.youtube.com/watch?v=soePsr0JdCk
きばいやんせ! (ganbatte in kagoshima-ben)