Application Enhancement, Scripts, Plug-ins
AfterEffects script that allows you to open a Final Cut Pro sequence in AE without export/render. Here.
AfterEffects script that will split a video layer at it's edit points. Magnum the Edit Detector. Here.
Utilities and web tools
Keepvid - Download Youtube source videos. Here.
VLC - Stable, multiformat video player, accepts more formats than QT. Here.
MPEG Streamclip - Very useful transcoding application. Here.
Avidemux - AVI container video editor, usefully labels I and P frames. Here.
Flip4Mac - Add-on that enables WMV playback and encoding within Quicktime. Here.
FFMpegx - useful multiformat transcoding application and video toolbox. Here.