i found American movies are more useful than BBC, or you can try DISCOVERY CHANNEL in NUSCAST.

visual and audio impact will give you deeper understanding, and easier for you to imitate.

another good point: some excuse to watch movies :D:D:D

most love stories are easy to understand, eg. how to lose a guy in 10 days, you can understand it very well in spite of the noise from the airplane ;) ;
war theme is a bit hard, involving those daily words but have totally different meaning in battle field~~~;
historical is mostly in old British English, like Brave Heart
kids movies are quite good, in terms of understanding, and humor

bear in mind:
the more you watched, the more good movies you will get and the more accents, and difficulties you will encounter~~~

yes. i love discovery, national geographic a looooot, but seldom watch animal planet~~~ :D