I like the books by Mary Sheedy Kurcinka. She takes a gentle approach, but explains it in a way that makes sense to people with a more punitive background. If you need to just get things under control, 123 Magic can be a starting point. It does use timeouts, and isn't as gentle as some of the books mentioned here, but it is a quick read, and has simple, straighforward advice. I think it would be a good start for a family that has been using physical discipline and can't see how to stop.
The vibe I got from some of the gentle parenting books I read was that basically I need to just cope with whatever my kid was doing without really explaining what the path would be to better behavior. But I haven't read any of the book mentioned here (except skimming a Positive Parenting toddler book).
I didn't like the Love and Logic books either-- too much of it was just mean.