Sins and Virtues of the Tongue?

I need your help.

Last Sunday, I began a new sermon series on "The Tongue of the Wise."  I want to teach on both sins of the tongue (grumbling, lying, crudeness, gossip, etc) as well as virtues of the tongue (encouragement, discretion, promise-keeping, etc).

What I'm wondering is what are both the sins and virtues of the tongue that people most need help with?  What topics would you like to hear addressed by this series?  

I have my ideas, but I really want to be as helpful as possible to our people.

A second, related, question is: what do you not understand about the tongue?  What is unclear to you about what the Bible teaches on the way we use words?

Thanks, in advance, for any comments.