Netbooks are generally small enough to fit in most any bag you've got, but if you want something small to carry around your Netbook (and your Netbook only), Timbuk2's new T-Pack does the trick. This bag can be used in one of three ways: as a standalone, padded case to be thrown in another bag, as a shoulder bag, or as a backpack-style bag, which in the above photo looks kind of ridiculous.
Along with holding your computer, the bag also has a zip pocket on the bottom that can be used to stash your power adapter, along with a few odds and ends like a wireless card, mouse, or USB sticks. The bag costs $30 and can hold Netbooks up to 10 inches in size, although buyers on Timbuk2's site report that some machines with extended life battery packs don't fit.