I think spanking's fine.

A woman last night was in my place of business with her four-year-old daughter who was having tantrums and making mom's life hard. I heard her speak to her daughter in a low, steady voice. I'm paraphrasing, but here's what she said:

"You don't talk to me like that, Amy. You know that's not right. You're going to get a spanking."

The little girl said back, "Don't spank me!" It wasn't a tearful protest, it was a willfull one. Reminded me of a certain friend, actually. Then the mother picked up her daughter and took her to the restroom. After a five minute absence, they both came back. The daughter was particularly silent but didn't look distressed. She wasn't humiliated publicly.

Parents should (and, IMHO, must) administer discipline that is just but firm. Kids should understand at an early age that actions have consequences... but they should also learn that might doesn't make right. And they should know that their parents would never hit them to satisfy their own anger. It should be a controlled act of caring, not an adult version of that same tantrum.