I've been using my 7D's built-in pop-up flash to control external Speedlites more and more. One problem with that setup is that the built-in flash is aimed directly at the subject. So even if it's not contributing to the exposure, it still get's in the way. The built-in flash will either inadvertently contribute some light to the exposure after all, or it will "blind" the model enough to cause some squinting or blinking.
The solution (for now) comes from Nikon in form of the Nikon SG-3IR. It's a shield for the internal flash that only lets non-visible IR light through the shield and thus doesn't blind the model.
Here's what it looks like:
The panel mount slides onto your hot-shoe and the panel flips down in front of the built-in flash to block the visible light. The front panel looks solid in this picture, but the fron of the unit has some slots to let IR light through that appear black, but are not.
Unfortunately, this panel will not work "straight out of the box". When the panel is in place in the hot-shoe, the camera thinks that an external flash is mounted and will not allow the built-in flash to be popped up. The solution is to grind away or cut out the right part of the panel holder that slides into the hot-shoe on the camera. If you look closely at the picture above, you can see where I cut-away part of the plastic. Doing this will prevent a micro-switch inside the camera hot-shoe from being depressed thus preventing the camera from recognizing the insert.
Here's a picture of yours truly in front of a mirror. There is a Canon EX 580 II on a light stand next to me bounced off the ceiling. The on-board flash is only used to trigger the external flash. But without the shield (or flipped up in this case), you can see that the on-board flash still contributes to the exposure:
Now here's the same shot again with the shield flipped down. The 580 EX is still being triggered without problems, but the on-board flash does not blind the model anymore or contribute to the exposure:
The SG-3IR is available online for around $12.
See, something good came out of Nikon after all