I was a member of Toastmasters for 5 years. They have clubs all over the Twin Cities (and the world for that matter). The only reason that I left was because I had a baby and my life got way to busy.
They have a well defined program to step you through speeches to become more comfortable giving a variety of presentations. You also have opportunities to learn about and improve your impromptu speaking, evaluation techniques, and even leadership skills!
I would recommend visiting a couple clubs in your area before joining one. Each club has a bit of a different feel and members in it for different reasons. You want to find a club that fits you and your schedule.
You can search for clubs at their website: toastmasters.org