Canon 7D w/ 100-400 L IS (and 2X converter) and a Canon HV20 mounted on top.
This was my set up back in May when I was in Titusville, FL watching the launch of STS-132. This combo worked great ... turned the video camera on with about 20 seconds to lift off and just let it run as I concentrated on shooting stills with the 7D. All worked well until I had to remove the 7D from the tripod because of the hight the shuttle was at and so fast. Video got a little shaky!
And it was very easy to set up to the same vocal point and it stays that way!
Hmmmmm .... wonder if I could mount the 5DMKII for video on top of the 7D for stills come the next launch? (never mind!)
note: I removed the 2X before the launch ... skies were so hazy and the 2X just made it worse