Youngzine is a great online magazine for students in elementary classroom--much news and other interesting information. Ties in nicely with Common Core.
TED (always love their videos--their app in iPad is great) now allows connecting YouTube videos with content for lessons. Lots of potential here...check it out.
PaperHelper is aniPad app that allows split screen--search web and take notes on other side ($1.99). This app really makes research online quite easy. Recommend.