Check out Catalyst: A Conversation Taskbook for English Language Learners
. It's completely self-contained with lesson plans, targets, review, assessment and a topic creation mechanism built in. Topics are relevant because they are created by the students themselves. Students are trained to respond spontaneously and will be conversing in a matter of seconds, sidestepping that messy little dance that instructors and students of such classes typically engage in while attempting to negotiate a topic for the day. Instructors will actually have very little prep to do beyond understanding the lesson du jour.
You can find out more here: http://www.speekeezy.ca/catalyst-the-book.html