Two iPad apps we use include:
A+ Spelling by Alligator Apps
ABC Reading Eggs (Australian website)
These are both recommended and used as part of my daughter's formal schooling. She is in grade one and is showing signs of mild dyslexia.
She uses Reading Eggs on her own and really enjoys it. I help to supervise the use of A+ Spelling.
A+ Spelling is very useful for preparing for spelling tests. I also use it to help with the learning of sight words. I think you'll find this one very useful.