Well, it depends on what you are going to do with your iPads.
The Apps I use daily are:
Office:
Pages - apple-made text editor, because I work with text a lot.
iZip - lets you use .zip files on your iPad, which is very important for me.
DjVu Reader - DJVU reader.
DocScanHD - lets you take a photo of a paper and convert it into a .pdf file, which is also very useful for me.
QuickOffice Pro HD - complete laggy crap but I didn't pay for it and I use it to edit .pptx files on iPad, not too often, tho. I heard that official microsoft office is coming.
Might need
Adobe Reader - not sure if it was free or not.
Dropbox - my personal favouite. Lets you keep a 2GB or even larger folder synchronized on all your devices. Able to read most common files like .docs, .txt, .pdf, .ppts and so on. Not a text editor, tho. Another great advantage is that you can open files in it, including .zip, .djvu, which it doesn't read and then share them with your friends by sending them links. Very useful when you need to share something and you are not home. It's free, btw.
Offline Pages - copy a Safari link, paste it into Offline Pages and download sites - in case you have a flight or you need to read something on subwa, or anywhere else where connection is not very good.
SpeedTest X - the speedtest-made app to check your internet, I guess it was free.
Google Chrome, Gmail, Google Maps, and Google Drive - 'cause I love Google.
And a number of English-ENglish, English-Russian, and German-Russian legal and regular dictionaries which no one else here needs.
Other:
Twitter
Skype
Viber
FaceBok
Pay Pal
SnapSeed and Skitch - photo editors
CalcHD - calculator
QuickMark - a QRR reader
Shazam - music identifier ("listens" to a song, shows you its name and artist, gets you a link to buy it in iTunes)
Maps With Me and CoPilot Premium HD - navigation
TripAdvisor and Booking.com - for travelling
Euronews live, Euronews, Euronews Radio, NatureJournals and Flipboard
A number of magazines and newspapers