In The Principalship from A to Z I describe a three-step process that you can use to promote teacher growth. It includes a planning or pre-observation conference, the observation itself, and a post-observation conference. A suggested process and prompts are included in Chapter "Q."
A recent article in Educational Leadership (Dec 2010/Jan 2011) provided another way to engage in really thoughtful feedback and support. Jenne Calasacco, a principal in Hyde Park, MA schedules a week of observations. It provides an extended observation over the course of a week and a set of conferences with the teacher. While my initial reaction was the challenge of allotting so much time to a single teacher, I'm persuaded that such a structure provides a more complete look at the teaching process and how the teacher monitors and adjusts their work.
I'd enjoy hearing from you about how you provide teachers with meaningful feedback about their work and how you engage them in thoughtful conversation about ways to refine and strengthen their teaching.