I'm amazed by the number of people I talk to that are shooting brackets for Exposure Fusion and HDR that don't use flash. If you shot brackets a single flash simplifies your post-processing! Over the years I've gotten a number of questions asking how to shoot brackets with flash. Below is my approach.
The first question is: Why? What's the point of using flash when you are shooting brackets? You thought the reason you shot bracketed exposures was so you didn't have to use flash, right? Well, the fact is that when you use HDR or Enfuse for interiors you tend to get low contrast results. That is, the blacks are not as black as you'd like and the whites are not as bright and crisp as you'd like. The term that comes to mind is muddy colors and dirty whites. You also have issues with white balance. It turns out that if you add a kiss of fill light from a single flash, it solves these problems. If you add a little flash to your brackets you don't have to spend as much time and effort in post-processing getting rid of muddy colors and dirty whites.
Here's my summary of how to bracket with flash:
To summarize: This technique adds the same constant level of flash with a single flash to each of the three brackets you shot. This fill flash is improving the quality of the light so that the whites are whiter and the blacks are blacker. This same technique works similarly with either brackets used for HDR processing or brackets processed as Enfuse.
For those that are already shooting brackets with flash, I'm sure you'll be able to add refinements or variations to this technique.