The Soma Fillmore is a grocery bag style pannier designed to please.  The Ortleib-esque hardware allows for quick and easy removal but with unmatched security and there is a handy carrying strap in case you need to take it with you.  And of course, it folds up and stores flush so it's not in the way when not being used. Sounds like a win, win, win to me!  Sold individually.