Must have iPad apps?

I see an Android thread like this, but no iPad app thread.

I picked up an iPad Air last week and am really loving it. I'm just curious as to what apps anyone may have found that they use daily or find really helpful. Games are okay, but I'm mainly looking for useful or productive apps.


So far I have found a couple.
Flipbook is great. Easy way to keep up with news, sports, tech, interests, etc.
Evernote is very useful. Create notebooks for various topics then save notes, pictures, documents, etc. in each. Basically an online version of a real notebook, and it can be synced to other devices or computers.
PCalcLite is a good free calculator app.


Then there are the obvious ones like iBooks, Dropbox, Netflix, HBOGo, Chrome, etc.

I'm also a bit of a TD5 Battles (Bloon TD game) addict.

 

Another decent one is AirDisplay. Turns your laptop into a dual monitor set up with your iPad.

It isn't as responsive as a true second monitor, but it is great for when you have to stare at a spreadsheet on one screen and be doing something else on another. Also, it is pretty awesome to only have to carry a laptop and and iPad to have a dual monitor display.