Althought there are a lot more out there, here are my favorites and ones I have installed on my iPad right now.
Created with Haiku Deck, the free presentation app
There are several I do not have but hope to have soon. I am excited that Microsoft Office is now available for iPad. (Currently I do not have enough free space to load the programs, but once I clear off the movies and pictures that are taking up so much space, I will be installing the whole MS suite).
There are also apps for the National Counselor Exam review, Remind 101, numerous games, relaxation apps, dictionaries, google +, reading, etc. While I have some of them, I do not use them extensively, so therefore they did not make it on my Essential List.
So what are your favorite apps? Let me know the top 5 you can't live without. Share your ideas below in a comment or join the discussion on Facebook or Twitter.