Even Apple app store cards are on sale.
Note: This deal is only good in store and is subject to store variance.
This week, Target is running a promotion in its weekly ad for 10% off "Select gaming cards" with a 'Minecraft,' $20 Nintendo 3DS/Wii U, and $20 Steam cards specifically listed. Elsewhere in the ad, Target is also offering 10% Apple App store/iTunes cards. These cards are essentially gift cards for their digital respective stores and are rarely on sale. The discount stacks (first 10% then another 5%) with the Target card's default 5% off promotion.
A trip to Target included visible discounts on Xbox Live and PS Plus membership cards, plus purchased discounts on PSN and Xbox prepaid cards. Your mileage may vary as just getting the visible in-add Steam card discount required some persistence.