It was noted that finding a well designed diaper bag is not so easy, so here are a few guesses.
*disclaimer, I don't have a baby, so I'm just going to assume that diapers,your iphone and lipstick go in these things;)
Diaper bag for the mister, here
Cute color for a leather bag, might not have the compartments one would want though.
Wedge tote, here
Quite a few of other nice color options here
by Pixelfolk, here