Stopping by the Fountain Square Goodwill yesterday, I saw a sign advertising a “frequent donor card” that you can request from a sales associate. Every time you drop off a donation to Goodwill, you can get a stamp on your card. Four stamps gets you a 20% discount on your next shopping trip.
You can also sign up for Club Goodwill online (except that the sign-up form is currently not working!). You are registered to win $50 in a monthly drawing. Goodwill also used to mail a discount in your birthday month, but I see that benefit is not mentioned any more.