Unlikely as it sounds, a company called Fleurville makes a very decent-looking dad-friendly diaper bag, if you choose the right material. (They finally introduced black canvas this month. Yes, they have camo, too.) The Alpha 7 is loaded with the baby-specific functionality found on their other bag, The Mothership. Also, it converts from shoulderstrap to backpack. Sounds heavy.
A good friend gave us Mum's messenger-style diaper bag, and it's pretty solid. A nice combination of function and unfluffy design. Check it out at Pokka Dot.
For 60 years, resourceful WASPs have been hauling any and everything in L.L. Bean Boat & Tote Bags, so why not diapers and bottles? You can get shoulder-length handles, a zip-top, and monogramming. And at only $24, you won't be dipping into principal, for which the kids'll thank you.
Don't call it a diaper bag; it's a a "dad field bag." What it really is is a Jack Spade messenger bag with a changing pad (and a sippy cup in the picture). Of course, you could just buy a changing pad and turn any bag into a diaper bag.