This is what I use, it is a Naneu Pro Echo. I really wanted a sling bag but couldn't find a good selection. My last bag was a Lowpro and I hated it, the design was good but the zipper failed after a short time of use and then it took 2 hands to open which was unacceptable when I have a camera in one.
I love the Echo. I have walked in the pouring rain with the bag un-covered (not on purpose) and the water-resistant nylon worked as promised. The outside was saturated, but nothing made it through to the padding. It works great for rides, I just swing it around and get in. Also, I have noticed that if I have the bag in-front of me it works as a perfect elbow rest when shooting. The only negative that I have had with the bag is the size of the straps. I am a pretty big guy (50 inch jacket size) and it was not loose enough for my comfort. But I put my mad sewing skills (this was my first sewing project

) to work and made an extension that works like a charm and doesn't look like it was an after thought. I called the manufacturer and told them my story and they sent out a couple sets of extra buckles free of charge so that it inserts/removes easily.
I typically carry my D5000, 18-55, 55-200, 35 f/1.8, external flash, sometimes a 2x telephoto extender, various filters/cards/batteries/remotes, plus a first aid kit and room for my wife to occupy with a few things.