Now I have always been a fan of Magic Lantern firmware, but I was pretty sure that the latest version of Canons firmware for the 5D MK II made magic lantern firmware irrelevant. After all it addressed the camera's major video flaw, sound, so why use a slightly wonky piece of 3rd party firmware?
Well, the latest beta version of Magic Lantern lets you increase the camera's bit rate. Normal 1080i hd video has a bit rate of 25mbs, the new firmware gives you up to 76mbs. That is a lot more information to work with. The thing that I like best about Majic Lantern is that you never install it in the camera. It loads off of the cf card each time leaving your camera firmware untouched. That having been said, if you brick your camera it is your own fault.
You'll need a fast UDMA cf card like this one to make the firmware work.
Download the firmware here