Meetup.com is a great resource.
If you are new to motherhood or just getting settled in a new neighborhood it is worth searching for groups in your area. Meetup is not just for moms… so if you are looking to connect with other aspects of your identity you may even find a non-mommy group.
If you already have a moms group and are looking for a way to infuse some new energy and use an existing internet resource to simplify the coordinating of details, tracking of RSVPs, and allow for folks who cannot make events due to work schedules, naptime, etc. to connect virtually without inbox clutter, meetup.com may be to tool for you. The message boards are simpler than most online forums, and you can set them so they are seen only by group members. At first glance, the cost to start a group looks steep, but if you succeed in getting folks to join you may be able to collect dues to offset the cost.