Spectronics, a company that focuses on Inclusive Learning Technologies, has put together this list of apps for literacy support. Not all of them are free, but they make great suggestions.
This is a great list of ways to curate content. Most of them also have apps. Diigo and PearlTrees work well on iPad. Flipboard is another great option.
The Virginia Department of Education helped to create this list of apps for students. You can download them from the Apple App Store. Some of them include digital texts from Pearson publishers.