Pelican Commuter Pannier 3
Pannier mounting details -- Klickfix mounting hardware installs easily and works well. There's a newer version available from REI, looks even more secure, but I haven't bothered to upgrade, this version has worked very well for me.
One note about racks: because this is a rigid pannier, peak loads against the rack stays are higher than with a soft-sided pannier -- when you hit a bump, there's no "give" in the pannier. I haven't had any trouble with my rear rack, but I've heard from another cyclist that his light-weight aluminum rack suffered a bent stay when hitting a pothole.