Easing Functions

EaseOut: Ease takes place at the beginning of the animation.
EaseIn: Ease takes place at the end of the animation.
EaseInOut: EaseIn takes place for half the animation followed by EaseOut.

There are several easing functions defined, although the user can create new ones deriving from EasingFunctionBase or directly from IEasingFunction

BackEase: Moves the value backwards by an amount specified through its amplitude before moving forward.
BounceEase: Creates an effect like a bouncing ball.
CircleEase: Accelerates the animation based upon a circular function.
CubicEase: Accelerates the animation based upon a cubic function.
ElasticEase: Uses springiness and oscillation to animate.
ExponentialEase: Accelerates the animation based upon an exponent value.
PowerEase: Accelerates the animation based upon a power of X time.
QuadraticEase: Accelerates the animation based upon the square of time.
QuarticEase: Accelerates the animation based upon the cube of time.
QuinticEase: Accelerates the animation based upon the time to the power of 5.
SineEase: Accelerates the animation along a sine wave.

Each of these has it's own properties to control the values, buy all can have an EasingMode set to one of the following options:

The following image is taken from the WPF documentation (http://msdn.microsoft.com/en-us/library/ee308751.aspx)