Ortlieb Bike Packer Plus
The Bike Packer Plus is a different take on the rear pannier than the standard Back Rollers. It has a drawstring closure and a lid, which some people find easier to keep waterproof and dustproof.
It also has a side pocket with a simple flip-down lid, that's useful for storing things you want to keep handy (like maps).
It uses the 'Plus' fabric, which is a lighter but still waterproof and abrasion-resistant Cordura.