Canon EOS 5D Mark II
As anyone will tell you, the best digital camera for video on the DSLR market continues to be the Canon DSLR EOS 5D Mark II. The Mark II was the primary camera that caused the industry to make the shift, mainly because of its incredibly shallow depth of field and beautifully stylized image quality. It has a full size CMOS chip and will do great in low light situations, giving you the detail you definitely want. It was very common for HD cameras to have a great amount of clarity and attractive imagery, but it often failed to have the film look that the Canon Mark II does.
Though the image quality is going to be stellar, you will want to use a non-sync sound system since it is not capable of actually recording anything worthwhile. At the same time you are going to have issues with the small CF storage space, so it may be important to keep a laptop nearby when filming so that you will be able to dump footage when necessary.
You will also really need to consider the price of the Canon 5D Mark II in that it is going to be the most expensive of the best cameras for HD video among the DSLR catalog, running over $2,500 in almost every case. This is before you pick up a lens package that could end up doubling that price if you have your way. If you are going to do this it is best to purchase the camera with some lenses for an elevated price, mainly in an effort to get a deal between the two.
The Canon EOS 7D is also a similar option to the 5D and can often produce almost a similar video quality, though not quite as expensive at a balance between $1,600 and $1,700 usually. You should note that it has the tendency to overheat; so filming in warmer situations is not a good idea.