The iPad will play movies, surf the web, and rock your tunes with ease, but if you want to use it as a calculator, you'll have to visit the App Store or possibly jailbreak your ipad!
Shift Apps's Digits Calculator for iPad is a powerful calculator that boasts some nice features, like a history scroll that displays a running record of all calculations as you perform with a flag button that lets you highlight certain calculations. Recently updated to 1.2.1, Digits Calculator has received a number of improvements.
The nicest feature in the new version is the ability to tap on any memory item and bring up a memory menu. The tape is a handy sidebar that keeps track of every calculation. Now, when you tap on a calculation on the tape, a new popup menu includes options to delete/edit/insert/total insert/use/flag the selected calculation result.
All the other calculators I have seen for the iPad are big wastes of space: Huge screen, tiny hard to press buttons! Not this one jumbo buttons, easy to press, and a paper tape that saves the results even after you quit with a clean refreshing design. I consider a calculator to be a useful/must have app for my new iPad since I can't add! :)
Digits Calculator is available for 99 cents from the Apple App Store