The critical components in choosing a lens for video:
1) Light - if you have the ability to bring studio lighting wherever you're shooting you can afford to get slower lenses, but if you're trying to run-n-gun in dimly lit environments you're going to want a 2.8 or faster lens.
2) IS - Stabilization makes a HUGE difference on handheld video (try a test with it on vs. off, it's night and day). If you have a stable rig this matters less, but again if you're going for handheld IS is pretty much a must.
Also keep in mind that 7D video quality is much lower than still shots, so differences in IQ that are vastly appreciable in still frames become less apparent in video.
How do you feel when using the 50mm? If you don't find yourself wanting too much more zoom then I would suggest the 17-55 IS or Tamron's 17-50 VC, depending on your budget. The 16-35 is a quality lens but probably won't offer a significant video IQ upgrade over the two options I mentioned to justify the increased cost (again, this is JUST for video, it'll obviously be a better performer when it comes to stills).
I think you'll find the 24-70 to be a little limiting on the wide end but it'd be a good idea to set a zoom at 24 and walk around with it for a little bit to see if it works with your shooting style.