I also recommend an Early Childhood PTA. I am actively involved in the one in The Colony. Our website is www.tcecpta.org.
Also, I met my now best friend through a mommy and me swim class at The Colony Aquatic Center last summer. She has a little girl that is a month younger than my daughter, so we've done lots of play dates and gatherings. Now we are doing more family stuff, since her husband and my husband are both sci-fi and video game nuts.
I know a friend who met other moms and kids through classes like Gymboree, Kid music classes, Library infant/toddler story times, and through church.
I tend to be shy and have a hard time seeking out friends, so these type of activities have really helped me meet other moms with kids my age.