I have tried some books for adults conversation classes. This is what you may have a look at:
JUST Listening and Speaking Upper-Intermediate
Speaking Extra (Cambridge Copy Collection)
Conversation by Rob Nolasco and Lois Arthur (Oxford University Press)
The Standby Book by Seth Lindstromberg (Cambridge)
Ways of Doing by P. Davis, B. Garside, M. Rinvolucri
But what I found really useful and engaging for my adult students was a listening series by BBC World Service 'Keep your English up to date. My students love it and can't wait for next parts. Each part consists of listening material of a new word, its origins and usage. Some of the words have provoked a lot of discussions. Here's a link.
http://www.bbc.co.uk/worldservice/learn ... /uptodate/