The 17-55mm IS is overrated, but it's not bad, either.
The Tamron and Sigma 17-50mm f2.8 stabilized lenses are like $600 or so and should perform just about as well. The Tamron has better IS.
If you're okay switching lenses, you can buy a set of primes (either on brand or using an adapter). 18mm, 25mm, 35mm, 50mm, and 85mm is the normal set for most dramatic video, but depending on your needs this can vary tremendously. A single fast lens in the 30mm range might be all you need most of the time and the kit lens is 90% as good as the 17-55m IS wide and wide open (similar resolution, slightly less fall off, less than a half stop slower in practice, etc.).
Pulling focus will be hard for documentary style stuff with any lens at like f2.8 or whatever. So if you're not doing narrative work and/or don't have a focus puller you might do better with a dedicated video camera or just accept the fact that you'll miss focus sometimes, which might be fine.
