Leo Babauta over at Zen Habits did me the favor of codifying most of the hard-won simplicity lessons I've learned in 4 years of being a dad, plus some I have yet to learn. The post, titled 25 Ways to Simplify Your Life with Kids, is simple, clear, and worth reading all the way through.
A few might be obvious to others, but were revelations when I finally learned them. Make cooking and cleaning a family thing. Get active. Focus on doing, not on spending. These aren't just feel-good Luddite aphorisms, either; he gives practical suggestions like setting up a single Google Calendar for the family.