Maybe this?  http://www.kinesisgear.com/c/C380C382.html

Don <www.donwiss.com/pictures/> (e-mail link at page bottoms).

I have a "slinger" type side/back pack. If you do not carry much in it they
are a bit faster to use than a camera backpack, but not all that much
faster.
You really should try before you buy.
If you carry alot of stuff and walk alot a genuine photo backpack is much
more comfortable. It is much kinder to your cameras than a regular back pack
stuffed with towels.

LowePro OffTrail 2 should do the trick.
I'm using either that or a Tamrac Velocity 9 when I don't need all my gear
with me.