I have a set of Jandd Mountain Panniers, which are I think are great. It has been raining a ton out here this year and I have been using Jannd Rain Covers to keep my gear dry.
They are large enough to cover all of the Mountain Pannier, even if you have stuffed it full of groceries or camping gear.
The Rain Cover is super bright yellow with reflective trim.
This is a view of the back of the Jannd Mountain Pannier, a small amount of the pannier is exposed to the elements. That part of the bag can get damp in a deluge, but nothing inside the bag has ever gotten wet. There is a drain hole in the bottom of the cover to let any water that gets in- get out.
The pack covers feature fully taped seams.
The rain cover packs down small, about the size of your fist.
You can check them out over at Jandd’s site: http://www.jandd.com/detail.asp?PRODUCT_ID=FRC-BIKE