The new Petsmart ad has an announcement about free samples given on the first Saturday of every month from 12 pm to 3 pm. There's also a little event mention on the Petsmart web site near the bottom. Check your local store if they offer this.
I think they've had this for some time, I grabbed some freebies on the first Sat of Oct. after reading about it in an email.
Not brands I'd normally feed (Purina and Rachel Ray) but the price was right.