Engadget spotted the Generator solar bag from Voltaic at CES 2008.
This bag features a solar panel that can produce up to 14.7W to charge your notebook, phone or other gadgets.
The "Generator" bag produces 14.7 watts from a single solar panel, but that's only with a full day of sun, so we're guessing you'll end up getting much less of a laptop charge with a normal day of use. In addition to a laptop plug the bag includes adapters for phones, USB devices and a car charger, and there's a battery inside the bag to improve the efficiency of the panel and to keep the juice flowing when you're in the shade.
Unfortunately the bag costs $599. If you really need more power for your notebook it will probably be more cost-effective to get a couple of spare batteries.