The rain-cover is made by EWA-Marine, a German company that makes a full line of covers and waterproof cases. I got this one for $18 USD from www.keepitdrycase.com

UPDATE: I've now used this cover in four very wet shoots, and it's my "new best friend". Not a drop of water got through to the camera. I've also learned that the cover can be pulled-back off the camera and up the camera strap during lulls in the rain.