If I were in the market for a new or my first diaper bag I would be purchasing the Not Rational diaper bag. Their bags are made of real italian cowhide leather, handmade in the USA. The diaper bags honestly look and feel like normal handbags and I WANT ONE!
Since they are a little pricey (they run just under $600), not many retailers carry them in stock, but they can be purchased at Kitson on-line, and at Barneys, Scoop, and a few other retailers around the country. Their most popular style is the Hansel (pictured above and below).
At 12.5 tall x 5.5 wide x 16 long, the size is very manageable and easy to carry over your shoulder or as a messenger.