Buzkids is a personalized app that helps little kids learn their letters, numbers, animal sounds, and fruit and vegetable names.
Star Speller, a spelling app for kids in kindergarten through second grade, has two games and a flashcard mode. Reasonably priced considering the features and content it offers.
Learning letters has never been as fun as it was with Alphabeast.
Yippee Cards is a cute flash card app with many sets that you can download for free.