Have students come up with a series of jobs and write them on the board. Next, ask various students which job they would rather have off the list. Ask leading questions to encourage them to justify themselves and discuss jobs amongst one another.
This is a good topic because people tend to have strong opinions on which job is the best. Some people want high-paid jobs, while others are content with a job in which they can wear cutoff shorts and work outside. These differences will inspire discussion, which helps conversation.
Everyone has an opinion on crime, including how to deal with it, and what causes it. Begin a class by asking students questions such as what they think encourages people to commit crimes; then ask other students for disagreeing statements. Soon enough, you will likely be hearing a variety of different opinions, and the strong emotional nature of this topic will encourage people to talk more.
While smoking has been unilaterally proven to be unhealthy, many people still smoke. If you have a class of adults, you can ask them if they smoke, and how long they've smoked. Move into discussions as to why they started smoking, what they think of smoking in general, and how they feel laws should address smoking. This is another topic that inspires debate because of the fact that peoples' opinions are often different from their actions -- many smokers will argue vehemently about how smoking is unhealthy, but still light up at the end of their class.
Families are a good topic too, since most people have profoundly different family experiences. Ask students what their families are like, what they enjoy about their families and what annoys them. This will often inspire by itself as people tell stories and give their opinions on how their families support them and, more often than not, irritate them.