I personally use a cheap $10 hip / waist sack that I picked up at Walmart that was suppose to go around your hip while you're jogging? Except I clip it closed and toss it over my head like a messenger bag instead. The one I got came with two spots to hold water bottles which I use to store extra lenses or a flash unit. I've even threaded my Gossen light meter case onto the front strap and have quick access to my light meter. And on the back strap I have attached a point-and-shot camera bag which I picked up for a buck and I store batteries, memory cards and a manual focus 50mm f2.0 lens in there. The only thing I've really done with this thing is added some extra padding to the bottom to help protect the camera when I put the bag down.
I've got tons of other camera bags. Big ones that just sit in my closet housing my sleeping gear. And one of those ones that swing around to give you access to your camera on the side. But I find I use this one 90% of the time, because when I'm wearing it, its like it disappears. Which is great when I'm carrying my youngest daughter around.
I'm actually looking for another one because I've got two separate camera set-ups. And I like this bag so much that when I want switch which camera I'm using I have to empty it and load up the camera I want to use. I'm going to break down and spend another $10-15 so that I can just have one for each camera set-up.
Just my 2 cents.