Working Mothers's Top 100 companies to work for is a great place to start, but bear in mind that it's just a starting point. Many of the self-nominated companies are advertisers in the magazine (paid advertising is, after all, their business model) and although they have verified these family-friendly policies in place, they don't apply to all locations, departments and job families.
For example, I worked for one of these companies that touted on-site pumping facilities. My particular role landed me on a client site where I shared an office with my client. I was not exactly in a position as a new employee to say, "excuse me, sir, would you mind vacating your office for 20 minutes every 3 hours while I, uhm, took care of business?"
Instead, work your network. You'll hear it time and again, but instead of looking at national lists take a look at your bus stop. Who's showing up in a suit and heels at 3:30 for pick up? Which parents are volunteering in your child's classroom midweek, where do they work? What do they do? ASK THEM! People are willing to talk, share their stories and how they've achieved some measure of balance. In fact, I'm willing to be they'd be flattered that you think they've arrived at a secret formula to work-life balance.
Ask for their card, send an email, take them to coffee. Then figure out to replicate that process in your own search.