Here are two of the latest from two of my favorite sewing blogs:
Gertie's New Blog for Better Sewing is having one revolving around Butterick coat pattern #5824. She lists her scheduled dates for sewing, and you have until October 1 to pick up the pattern, fabric, and notions if you want to join. As of right now there are 170 people joining on her Flickr group.
And MPB is having his own, too. His doesn't revolve around a pattern but a theme instead: Halloween costume sew-along. MPB's doesn't start until October 10th so you have some time to figure out what you are going to make. His Flickr group will be started later, so check back for the address when it is available.