The Sony PlayStation Network offers a free$20 credit when you spend $100 on the PlayStation Store in the month of October. That's the best such offer we've seen from PlayStation Network. (We saw a free $6 movie credit last fall.) According to the responses in the comments section, the credit will "expire in December" and you'll have "about a month" to redeem it after it is applied to your wallet. Each member can earn only one $20 credit.