Mentioned earlier was Ease and Wizz, an AE palette for new easing types. The script is basically the same in 2015, though with numerous incremental refinements. Here's the latest demo video:
Back in 2009, Ian Haigh announced the script on the AE-List:
I'm pleased to announce version 2.0 of Ease and Wizz, the After Effects palette for smoother easing. If you're not familiar with this script, it's an adaptation of Robert Penner's easing equations for Flash, and gives you more options when you're tweening values such as position, rotation, or scale.
The big change in this version is that now you can tween along a curved motion path, which was previously impossible (the expression would effectively ignore the bezier curves, and the resulting motion path would be linear). Also, you can now apply easing expressions to mask paths and shape paths. I call this monumental addition "Curvaceous" :)
It's available for (FREE!)
Note that when using Curvaceous, you will no longer have access to Back and Elastic tweening. The (slightly techie) explanation for this that rather than tweening the actual *value* of the property, Curvaceous tweens the *time* of the property, using the valueAtTime method. As the Back and Elastic easing types actually overshoot the original keyframes, Curvaceous has no way of knowing how to extrapolate the extra data to move past the last value. Simply turn off Curvaceous if you require Back or Elastic (the palette updates when you toggle Curvaceous, so you don't need to commit this to memory).