canon are the way to go if you want a DSLR for filming, Nikon and pentax dont cut it when it comes to the sensor quality for video, while they are great for still life. furthermore, canon actually makes camcorders dedicated for filming, and I believe they do so with the same sensors as some of their DSLRs. Sony might be your other option, but you probhabhly wont get as good DSLR vid out of a sony DSLR camera for the same price, youd have to go for a dedicated camcorder, where you are then stuck between choices of canon, sony, panasonic and more, weighing lens interchangeability and other factors in.
All in all, ill give you a bunch of money if you find a good amateur filmmaker using a nikon or any other than canon for their videos.
for canon, the real video beast would be the 5d, it has been the go to video DSLR for anyone serious in the concept. (MKII and III that is.)
good luck on your hunt, take anything into consideration, from how long will you be using a lens with future cameras, to price/performance points. And always remember, a cheap camera with good glass will make better quality than a 1D with cheap glass, plus your digital camera will always end up outdated, while a good Kit of L glass wont need replacing for a loong time.