In reply to Joel.

May I suggest we try keeping track of brands which we think haven’t (yet) shrunk their contents? Perhaps it could serve to express consumer appreciation, some encouragement and spread the word.
The nonprofit Cornucopia publishes scorecards which emphasize what they consider to be true organic foods, as well as a chart of formerly independent organic businesses now owned by larger corporations.

Off the top of my head, I think Organic Valley still has half-gallon milk.