A friend of mine has done two excellent iOS Apps called Core Physics and Core geometry, that are free of charge until Friday May 29. It is two very well made Apps for students and professionals about physics and math:
Core Physics (iTunes)
Core Physics is the perfect tool for students, professionals in the fields of mechanical and electrical engineering and physics enthusiasts alike. The simplicity and functionality of the user interface is the basis of the design framework for Core Physics. The application uses the data provided to solve mathematical physics problems. Just enter your data into the fields provided, leaving only the field which you want to calculate blank.
Core Geometry (iTunes)
Let's say that you want to find the volume of a cylindrical drum or that you want to calculate the distance between two points on a map. Core Geometry is a mathematical application which aims to solve geometrical problems quickly and reliably. Simply input the know values into the fields correlating to the 2d and 3d diagrams provided for each problem.
Please go and check them out, they are really worth that.