External Pop-up flash. Great Idea. Not radio controlled. Light controlled.
This means that it has to be pretty much line-of-sight. Not 100%, but close. If I could get internal radio control in my Canon gear I would pretty pleased.
That said I like the pop-up flash feature on the 7D.
First usable picture does not fit the usual style of this blog. But it shows the effect well.
The pop-up did double duty as both trigger and fill.
100mm Macro Femail@example.com