Things is the new app of the week on the App Store. We are facing one of the best GTD (task manager) there is for the iPad, although it is also one of the most expensive.
Things offers a balance between ease of use and functionality, thus avoiding that the application lacks basic functions or is too complicated to use. In this way you can keep track of tasks, notes, specific dates and projects.
The application has interesting features such as smart lists or the planning function so that we work in the most efficient way possible.
If you want to see the interface of Things for iPad and know how it works, the following video will help you answer your questions:
http://www.youtube.com/watch?v=NVruDH16tRc
Things for iPad is a really complete and well-made application, but its price may be excessive for what you are looking for.