I have a Knog bag that works either as a messenger bag or pannier with a cam-lock attachment. I use it mostly off the bike and nobody would guess it's a bike bag. As a pannier it is adequate, but this isn't something you'd go cross country with, just as a commuting bag.

Now if I could get the rack off the bike my son took with him I'd be all set. In the meantime I'm using a backpack because I don't really like riding with the messenger bag on my shoulder as it doesn't stay put.