Tales 2 Go is our favorite ipad app, and it's for sale on Homeschool Buyer's Coop!!!! It's a little pricey, but I was able to buy a couple of years subscription before the price went up last year. My girls listen to audio books every day via Tales 2 Go. They especially love listening to the American Girls books. Check out this deal at Homeschool Buyer's Coop.
It's free to join and if you put "cheerios" as your referral code, I'll earn a nominal fee when you make your first purchase. Thanks!