EDIT: I have created a standalone page of updated freebie newsletters you should be joining!
I posted a list of places that I suggested signing up with last March. The tl;dr version is that freebies occasionally appear which are only available to people who signed up in advance. However I wanted to raise the point again because one company has been killing it lately.
Over the past month, General Mills has offered a ton of free cereal to people who are on their Pillsbury, EatBetterAmerica, & Betty Crocker newsletters. If I were you, I'd join all of them with my freebie e-mail address and then you'll be eligible for the samples when I start posting them from here on out. It's hard to pass up free food.