Backpacks are cool again, and not only for the Kindergarten set. Leave the stuffy briefcase at home; for laptops, nothing beats a padded backpack. The same goes for a contemporary twist on the diaper bag. After all, who wouldn't want to be hands-free for work, for school, or for traveling? In the sleekest silhouettes and materials, the chic new wave of women's backpacks makes slinging one on downright irresistible.