Check out the Thule photo backpack.
I looked at a million of these things and all the ones that held enough looked freaky clumsy on. Sticks out too far and/or is too wide across your back, making you look awkward. And the few that looked cool, like hiking stuff, were only 1/2 for camera stuff, and the other half for camping junk.
Opens like the Lowepro Flipsides (from back).
Unique in that it is no wider across your back than necessary, so it does not look like you have a giant slouchy thing on you. But also has a very large capacity compared to bigger-looking packs.
Thule is great at waterproof camping gear and packs, so this one is serious.
Looks great, like a hiker.
Has a fold out cover.
Doesn't scream "camera gear in here" with ether its looks or its brand name; looks like hiking stuff.
All that, yet still holds a TON.http://www.thule.com/en-us/us/products/sleeves-and-cases/camera-bags-and-cases/camera-backpacks/thule-perspektiv-backpack-_-tl_85854227995_v2