I'd add that iTunes credit is not just good for iCloud storage, but for iTunes Store downloads of music, movies and tv shows; Apple App Store purchases; and subscriptions through your iTunes account like Netflix (and I believe Hulu). When Netflix finally got around to raising the price of our grandfathered plan last month, I canceled my subscription through Netflix and restored it as an in-app purchase through Netflix on iTunes. So now my monthly Netflix subscription is debited from my iTunes credit that I always buy at a discount.
A 15% discount on iTunes gift cards is pretty standard and these deals seem to pop up at least once or twice a month. I know Costco frequently sells a $100 pack of iTunes cards for $85. This PP deal lets you in on a discount for lower denominations ($25). 20% off happens often enough, and I see 25% off usually during Black Friday and the holidays. (You can follow
http://twitter.com/itunescarddeals, who posts current iTunes deals.)
One more thing -- If you plan to buy iTunes music, movies or tv episodes or Apps, go through Ebates for 7% cash back! I don't think it works on subscriptions,