The F12 Action Cache contains over 30 stock effects, all in .Blend format.
Blend That Film writes:
This is a library of stock effects such as Muzzle Flares, Bullet holes, Bullets, Explosions, Dirt, Debris, Sparks etc. For use in live action compositing and 3D Scenes. The entire pack is created from scratch with textures and environment mapping included and you can download it 100% Free from Blendswap.com.
Here's an overview video of what the F12 Action Cache contains and how to use it.
Blend That film is also back with some excuses in this new video.