Backpacks are handy for several reasons - they are great to use while baby wearing, make subway trips a whole lot easier, allow you the use of both hands, and depending on the style, they can easily be used as a unisex diaper bag.
1. Twelve Little is a great brand all around. They make fashionable and functional diaper bags and accessories. I really love their Companion Backpack which is waterproof and designed with lots of interior and exterior pockets.
2. I'm a huge fan of everything Baggu. While they do not make a traditional diaper bag, their Classic Backpack is an everyday bag that can also be used for toting around baby. It's lightweight, can be used for multiple purposes and dad won't mind slinging it over his shoulder as well.
3. KAOS is a Norwegian brand that specializes in unisex products for parents. The Ransel backpack has a super roomy interior and a total of eight pockets to help keep you organized. But the best part, a built in strap allows you to hang it on any stroller.