Welcome!
'Must have' apps? Mmm, there are so many for me...
Google app for iPad. Do not miss the voice search functionality. It's impressive!
Google Earth.
If you like cinema, IMDB (This is probably the best app ever from the usability perspective)
DropBox
FaceTime, which is way better than Skype and it comes with the iPad so you don't have to pick it up from the App Store.
Evernote
Wikipanion
WordReference (iPhone)
Weather forecast apps (local apps)
Transport service apps (local apps)
Radio stations (local apps)
These are my 'must have' apps.
Do you like games?