I have yet to find one that I'm happy with...but those at Allen Fly Co. look somewhat promising.

personally, I like having the space in back for my raincoat, lunch, a beer or two, and my DSLR plus the hydration bladder. I currently use a very small vest and throw the backpack over the top of it, it isn't ideal but better than anything else I've used. As far as actual flyfishing gear, I don't take much at all so it's not really for that.