Check out AGU bags from the Netherlands. Weatherproof, several have built in or detachable map pouches. I've had one for a couplafew years and it's good. Protects my camera gear, rain or shine.

Detachable shoulder strap, so it's not in the way while riding.

The KlickFix mount system is very handy. However it makes the bag sit up a bit higher, so it may block some handlebar mounted lights and accessories. When I use one of my video cameras mounted on the stem I can add an extension so it sits higher than the bag.

I don't think there are any AGU dealers in the US but it's easy to order from Europe and the exchange rate is still pretty good.