Motherhood Later than Sooner is a group for moms who have children at the age of 35+ (which probably includes most of NYC). Meet other mature moms at playdates, family outings, moms night out dinners, and more.

Big City Moms is one of the biggest mom groups in NYC. They host lots of different events, lunches, dinners and seminars for moms, families and moms to be including mompreneur dinners, mommy and me work-outs, preschool seminars and more.

Hudson River Park Mothers Group organizes free play groups, as well as educational and social events for mothers, children, and families residing in Lower Manhattan and the West Village (Anna from HRPMamas says that the West Village group has split off and is now West Village Parents. They've also started a Lower east Side Parents group.)

Meetup.com is a national site that hosts every kind of meetup group. You can search by kind of group you are looking for and location. There are lots of New York area parenting groups listed including nursing mommies, stay at home moms, single mothers, and MILFs, and if you can't find the group you're interested in you can start it.

Metro Moms Network members share information and ideas on the group's website. Events include lunches and happy hours for moms, family playgroups, lectures on subjects of interest, and family parties.

Bowery Babes, mostly Lower East Side and Soho moms, have parties and potluck picnics in local parks and restaurants, two art classes at the Lafayette Street Childrens museum, excursions to museums and galleries, music classes held in several private loft homes, as well as lectures on sleep and the environment, and occasional Mommy Beauty Mornings at Bloomingdales Soho. The website contains passionate discussion about "alternative" lifestyle ideas as well as green products.

Park Slope Parents is a group of local parents dedicated to supporting the families of Park Slope, Brooklyn by providing a way to exchange information about parenting in our community with a yahoo group, events and a website.

The Bronx New Mommies Group hosts monthly meetings, educational workshops, tele-classes, and seminars where moms come together to socialize, discuss, and tackle common issues related to motherhood, children, and parenting.

Soho Parenting hosts parenting groups that balance developmental information with guidance about the emotional work it takes to be a thoughtful parent, as well as being a place for parents to meet and form lasting friendships.

NY Moms Connect is an relatively new online social community for NYC moms and expectant moms with forums, blogs and more.