If you’re so inclined to spend $100 on the PlayStation Store this month, you can get $15 back in credit. Anything will count and the promotion is already underway, so just buy whatever and you’ll work towards it.
Also, you can pre-order games digitally and it will count towards your $100 total. Though I heartily recommend not doing so in case your favorite AAA game under-delivers at launch. Also note that the deal technically ends on October 28th, so don’t push $99 after that point and lose out.
Get $15 for Spending $100 or More on PS Store [PlayStation Blog]