Gizmodo points to the review of the Kata R-102 photo rucksack at Shuttertalk. This one cool bag to consider for $125 USD.
I am currently using Vidpro VID 100 Durahyde Video/Photo/Digital Camera Bag ($34 USD), which I find very comfortable and big enough for all my gear. I don’t have that much of it yet though, but there is plenty of space still. I doubt thought that it will suffecient for two cameras plus lenses and flash units. When that time comes, I’ll be looking towards waht Kata has to offer.