Lowepro make a great selection of backpacks in all sizes and "Slingshot" packs which is basically a pack that goes over one shoulder and across your chest so that it can easily be slid around to the front to get your camera out. You can check out their selection of products at
http://www.lowepro.com/products/
Oh and almost all the packs come in black and a lot of them are weatherproof
hope that helps