When I wanna go incognito, I just throw
a Zing around my camera & lens, stuff a second lens in a padded lens case, and then pop them into a regular backpack or bag (usually a timbuk2 Metro).
The Lowprowe Compudaypack was too bulky for me, (also the Crumpler $6M --not to mention that damn velcro screams every time you try to take something out of it). I usually use a Kata Sensitivity V, but it's a high-tech James Bond backpack, no mistake.
Your best bet for looking like not-a-camera-bag is probably to use a non-camera bag, and kit it out either with padded cases & covers for individual items, or with
a padded insert.