I'm not sure. I've been wondering that myself. I am working on joining a moms group, but I'm not sure if that is going to be what I want really. These moms are all stay at home moms and I am a single working mom. We'll see I guess.
The great thing about a mom's group is that you all already have something important in common- you all have children who are usually around the same age. I live in a smaller town with not many options so I find that some moms have many similarities to me while others are very different. There are a lot of organizations that are directed towards certain moms like La Leche League for breastfeeding moms, or MOPS for Christian moms. It doesn't hurt to try a few and see where you feel the most comfortable!