Saw the "Targus Unofficial" netbook bag at our local Walmart (Canada) for $19.99. Vertical and has a small outside pocket for mouse or charger cord.

I have this bag from Mountain Equipment Co-op (also Canada) $19.00 and my 11.6" netbook fits perfectly (while in it's neoprene sleeve) into the slip compartment at the back of the bag, then all my other electronics (digital camera, power cords, etc) go into the main compartment.