One good thing about the new Black Magic Cinema Camera is that it can support IS (Image Stabilization) in Canon EF mount lenses. One not-so-good thing is the smaller sensor that will need additional attention for wide angle video. With these two things considered, the first lens that came to mind is the Canon 17-55mm F/2.8 with IS. This lens receives excellent reviews (not for Full Frame cameras) but will run you almost $1200 dollars (as seen here).
Canon 17-55mm F/2.8 IS Lens
After doing a bit more research, i've come across the Sigma 17-70mm F/2.8-F/4 with Optical Anti-Shake Technology (image stabilization). It's not quite as nice as the Canon 17-55mm because it can't maintain the F/2.8 aperture, but it does have a bit more reach and i'm typically stopping down the aperture to an F/4 anyways. The Sigma receives an almost full 5 Star rating with reviews, and is currently On Sale at just $299 for the next 15 days.
Anyone with a cropped sensor Canon DSLR such as a T3i, T4i, 60D, 7D, Black Magic Cinema camera, or even Sony FS100 / FS700 shooters may really want to take a look at this lens. Even if you just consider this a constant F/4 aperture, a 17-70mm Image Stabilized lens for $299 is not a bad deal. Check out the sale via B&H (click here).
Sigma 17-70mm F/2.8-F/4 OS HSM Lens