If you are looking for a DSLR top light, I would highly recommend the Tecpro Fellini Click LED Camera light. It is very lightweight but has some serious power. The light has a dimmer switch so you can get the right amount of light you need. It also comes with coloured panels which magnetically clip on, so you can easily change the light from daylight to tungsten. It has a ball and socket head which will fit on the hot shoe on top of your 7d or 5d. For power you can either run if off 5AA batteries or you can attach an old Sony video battery (any of the following LF570, F770, F970 ,F550,F750).
I used this the other night on a shoot for the BBC. The presenter was sitting in a car, and needed to be lit gently enough so it was still possible to see the small amount of light in the street as well as the presenter. The Fellini click was perfect for this, I could just set my exposure to capture a small amount of the scene through the window and then dial in enough light so the presenter was well lit.
If you want to buy one from the UK I bought mine here.
