sign up for the cardinals email that comes out each week. It will usually have a code for the next week or two games (usually half off tickets somewhere in the park)
also taco bell has a b1g1 code out now and I still have some mcdonalds codes that we never used (plus a 10% off coupon we got with our tickets earlier, plus 2 free tickets we still haven't redeemed from the opening weekend giveaway)