When Wolfram Alpha first launched its iPhone app, the powerful features were overshadowed by the massive $50 price tag. Wolfram has now dropped the price of Wolfram Alpha for iPhone to $1.99, as well as announce an iPad version of the app. On the iPad, Wolfram Alpha offers all the same computational abilities and data, while taking advantage of the bigger screen and features like map integration. The new version also does arithmetic right in the search field, and saves your results for offline viewing later (which is important for wifi-only iPads). Wolfram|Alpha App plugs directly into the Wolfram|Alpha supercomputing cloud, computing answers to your questions quickly, efficiently, and without scalding your lap.
More info: Wolfram|Alpha