Just for your reference.
I'm using Lowepro's Inverse 200 AW. (Not pricey)
It's a sling + belt pack. It lightens the burden on my shoulders because I carry it in both Sling & belt it as pouch at the same time.
No need to use one leg for support when accessing lens or camera.
btw, I'm using it for 50D w/ grip, tokina 11-16 w/ hood, 85mm w/ hood, 35L or 24-70L w/ hood, and a nissin di866 flash (Flash bag mounted side of the bag)
Together with a lens cleaning pen, blower, flash stand, spare batts, cable remote, wireless trigger transmitter & receiver, etc
There should be better products out there probably already mentioned by the above replies.
But so far, this is kinda good & very suitable for me personally.
http://products.lowepro.com/product/Inverse-200-AW,2101,7.htm
[video=youtube;tqjPDQPO-qk]http://www.youtube.com/watch?v=tqjPDQPO-qk[/video]