I'm a city-dwelling creative and I totally get your search for a good-looking yet discreet bag, most of them look terrible or completely obvious as a thief-target. I agree with the commenter who said you probably can't carry all your gear at once (I assume you know that) and I also agree that a one-shoulder sling-bag/messenger bad will get heavy and uncomfortable, more than you think. I originally got a LowePro 200 because I wanted something ultra-compact but good-looking. It's nice but if I carry more than my XSi + 24-70mm (which is about as heavy as a 70-200mm) my shoulder is aching by end of day. The sling look isn't worth it in my opinion, and I'm pretty in-shape.
That said, I recently got the
Kata KT DR-467as a gift and it's nice. The all-black outside looks cool and like a regular backpack. The sealed zippers are very helpful in bad weather, yellow insides help you see black lenses in low-light, the laptop pocket is big enough for a 17" MacBook Pro, it's got removable panels like crazy, and a really well thought-out amount and placement of extra pockets. Now, I don't know if the pockets on that will be big enough for your 70-210(?) but it fits my 24-70mm on-camera with enough room to fit my 50mm in the next panel-pocket over. The top is possibly as big as the bottom... you could probably fit four 580 flashes in there, no joke.
I'm not saying my bag model is the one for you but the quality and architecture from Kata is extremely high.