A great time-saving preset to "duck"(fade in/out) a music layer based on a voice over.
"Ducking - Audio Terms Explained - Process of automatic compression, eg when the announcer's voice signal causes the level of music to be attenuated."(from lp2cd.com)

Film Burn is an Animation Preset that automatically creates the overexposed "roll-out" effect, where the tail (and the head if you want) of a clip flickers into overexposure. By Stu Maschwitz

Create your own dynamic transition effect in After effects, Simple techniques along with Particular will be explored

Simulate water effect as if its sliding down the glass surface

Emit lots of footballs and make them bounce in After Effects. Trapcode Particular bounce option will be the weapon of choice

Randomly shifts the selected layers in time within user defined range.

A practical application of a layer space transform.
Not very new, but still very useful.
by Dan Ebberts's resource for After Effects scripting and expressions

With this preset you can prevent "CC Light Rays" to cause a light spot if it's not over an opaque part of a layer.

With this preset you can cause the opacity of a layer to control the brightness of a "Lens Flare".

If you want an abrupt change in value, but not on every frame, you could use this expression.