Any tips for free discussion classes?

Hi there,

I wonder if anybody could give me some hints about this issue...We've decided to work this out in a class: we set a topic, mostly a socially controversial one, and encourage Ss to give their opinions. We seldom make any corrections while the discussion's going on, but take just some notes on their mistakes. What we really mean to do is to help them develop some techniques for say, gap filling, turn taking, agreeing, disagreeing, etc. But the problem is, whatever source we've used so far sound so formal (as they're mainly intended for the Ss getting prepared for exams and interviews) that Ss feel not willing to use them at all. Is there any reliable source where we can find the Expressions and Phrases native speakers use in their daily speech? (possibly in the right context to make the Ss sure of their usage) Thanks in advance.