I am using the Lowepro DSLR Video Fastpack 350 AW. Works great for my needs (which are not video, but photo - I just found this bag to be the best fit).
The photo compartment usually has:
- 5D Mk II with grip and the Canon 16-35 lens attached.
- Canon 50 mm 1.4 lens
- 2 Lumopro LP-160 flashes
- Zoom H4N sound recorder in protective case
- Lens and camera cleaning gear + air blower
- Interfit iSync 4 strobies kit
The top compartment carries spare lens caps and hoods, a 500GB hard drive, USB cables, filter pouch with 6-8 filters - and on days where I need to carry the Canon 70-200 2.8II IS, I can comfortably fit that up there in its own (very sturdy) bag. This still leaves room for a bit of lunch.
Water bottle goes on the side of the pack.
The built in sleeve - which is well protected - has room for my 17 inch Macbook Pro.
And being part of the AW series it has a rain cover located in the base of the pack. Good as snow cover as well
Fits most of my trip and backcountry needs, and I have yet to see any issues even though most of my backcountry trips are on my snowmobile in rugged terrain up here in Greenland.