It isn`t that easy to find an interesting documentary, movie or book about the German Democrativ Republic in English. Therefore I would like to recommand you two english movies about the live in the GDR.
The Lives of Others: Won an Oscar in 2006 as Best Foreign Language Film.
Good Bye, Lenin!: A movie from 2004, very funny! (German with English Subtitles)
More books and DVDs about the German Democratic Republic you will find here...