There are many bags out there, but here's a review for a bag similar to one I've got
http://www.shuttertalk.com/articles/katar102
The review is for the R102, I've got the R103 which has an additional pocket for a laptop. I don't pack mine as heavily as in the review, but can easily fit 30D+grip, 12-24, 17-85, 50, 70-200, flash, portable storage device, blower, filters - just for rough sizing.
My only issue with it is when I forgot the zip up the centre pocket and my camera/lens fell out. Otherwise I like how it has got the tripod holder for travelling (if they let you bring it on the plane).
There are so many choices of bags out there, make sure you try them on to make sure they are comfortable.
As mentioned in other threads, you can get different types of bags.
I find the backpack easy and comfortable to carry around all day as the weight is evenly distributed across both shoulders and it's well padded, but if you're into changing lenses, and changing things from the bag inside, it's a bit troublesome having to take it off and put it back on all the time - that's when a shoulderbag or othertypes can be a bit more convenient, The downside with shoulderbags is that a day of carrying a full shoulderbag all day can cause a bit of pain.