I also love the Starfall ABCs iPad/iPhone app. My daughter has been using it for a while and she loves it. It is just the alphabet portion of Starfall but it the exactly the same as it is on the computer! They also have a Learn to Read app as well as 4 other themed apps that are also on the Starfall website.
Another neat thing about Starfall is that they have free downloads. I love to use the ABC Printouts with my kiddos when we are learning letter sounds. It's really great because the correspond with the pictures and words used on the website/app as well.
If you haven't already go check out Starfall! You'll love it!