TED TED talks have become extremely popular for educators and professionals world wide. With this app you can pull up TED talks from scores of live events. So much great, free information.
Wikipedia When you need information quickly, be it for lessons, papers or tests, wikipedia is great. It's easy to search, the pages load nicely, and you can bookmark pages.
Socrative Teacher This is a really cool student/teacher interactive app that can be utilized in the classroom. It comes with learning games, is easy to set up, and because of real time results, it really saves time in the grading process.
Teacher Aide Pro Even though it is pricey, I recommend the pro version of this app. It's awesome for keeping organized. It works as an attendance record, grade book and the ability to email students or parents regarding their progress.
NASA App Love this app from NASA. It's awesome for teaching my kids about space. I use the news articles a lot, and like that I can email them to myself, print them out and pass out in the classroom.