These are the tools I use in my physics classes that are specific to physics
Paid iPad app: http://itunes.apple.com/app/wolfram-physics-i-course-assistant/id443476961?mt=8&ls=1&uo=4&at=10l6SU
Paid iPhone app: http://itunes.apple.com/app/wolfram-physics-i-course-assistant/id443476961?mt=8&ls=1&uo=4&at=10l6SU
Paid iPad app: http://itunes.apple.com/app/wolfram-physics-ii-course/id455760886?ls=1&mt=8&uo=4&at=10l6SU
Paid iPhone app: http://itunes.apple.com/app/wolfram-physics-ii-course/id455760886?ls=1&mt=8&uo=4&at=10l6SU
Website: http://phet.colorado.edu/