I teach English Immersion and I sometimes have a special day where I pick a topic like animal rights, enviornment etc.  I sometimes invite guest speakers who are very familiar with the subject that has been chosen.  Usually the people that come in are people I know, or friends of friends who are willing to come in without charging a fee.  I have had people who work with animal rights come in and speak about animal rights.  People who work with the enviornment come in and speak about the environment.  My students love this and always look forward to a guest speaker.  We start earlier by learning the vocabulary, reading a story on the subject and preparing questions for our guest speaker.  You would be surprised at the number of people who are willing to come in and share their knowledge for free.  After the speaker has left we have a class discussion.  I find that this stimulates  the students, and that they are not only learning the language, but are learning about important things in life as well.