I just bought the Seattle Sports Rain Rider a few weeks ago and have commuted with it almost daily for those few weeks. It's been great. Easy to carry, easy to clip on and off, and the lower brace rotates so it fits on different rack struts. It's waterproof, but I haven't ridden in the rain yet so I can't attest to it's effectiveness there.
Check it out here:
Amazon.com : Seattle Sports Rain Rider Pannier Bike Bag : Bike Panniers And Rack Trunks : Sports & Outdoors