While Wikipedia is far from the gold standard of research sources, it does give a good general overview of topics and in my experience is quite well-written. It therefore is a helpful resource for developing reading comprehension, background knowledge and use of strategies for vocabulary and breaking down expository text.
I discovered Wikiweb, which displays articles as semantic web connections between ideas, because it was free at Starbucks, but at $2.99 I think it's still fairly priced. It's got a beautiful look and feel and the added feature of displaying visual connections between topics is potentially very useful for therapy. The articles as displayed can be selected in order to activate Speak Selection, so they can be read aloud as well.
This video from Wikiweb is a bit strange, and makes it seem like you should use the app just so you don't become Claire Danes in Homeland, but it gives you more of an idea how the app works.