I am getting ready to shoot a short feature with the 7D. I have a great deal of HD gear including 17" and 9" Panasonic HDSDI monitors. I am going to try to use an AJA HDMI to HDSDI converter to feed a monitor for the director and camera operator.
This should fit your needs nicely. Keep in mind it needs a power supply but you probably noticed that. Nice thing is that it actually has 2 HD/SDI outs so you can simultaneously go out to 2 monitors. Very handy.
Also... while the other cannons down-convert upon recording you will find the 7D does not. While it is not a "clean" 1080p signal it is a nice hi res version (Not sure the exact specs) that looks great on an external monitor.