If you like scrumptious leathers, I'd definitely consider the Not Rational diaper bag. The Susan Fitch Million Dollar Baby bag is great too - cool looking with lots of grommets on the pockets. For some really interesting styles and great organization, Mia Bossi is the great. There's also a really interesting leather diaper bag by Suzy Hammitt with studs galore, but people have said that it's too heavy to use all the time.
If you don't have to have leather, the Oi Oi and JuJuBe bags are cute and really functional. And as a previous poster has said, the Petunia Picklebottoms are a classic. If you like cutesy patterns, the Lesportsac Tokidoki Cucciolo is a winner.
You also always have the option of using a large designer bag (Bbag work bag, Chloe Tracy or Betty) and using a Diapees and Wipees or Royal Heinie case to organize your baby stuff.
You can find tons of information on the yahoo group babybags. The mamas there swap and sell bags to each other all the time. I've been on there for over 2 years - it's a dangerous place, almost as dangerous as this one!
Here's the link:
babybags : The Diaper Bag Search, Sell 'n Swap!
Also, check out the Mommies with Style blog. They review all kinds of trendy baby items, not just bags.
HTH!! And congrats!! I have tried out most if not all of these bags myself, so please feel free to PM me with any questions.