Since Linux is used a lot in the film effects world, its users are blessed with many proprietary node-based compositors suitable for heavy-duty compositing work. The most affordable ones Apple Shake, D2 Nuke and Eyeon Fusion. All their price-tags are around $/€5000. The other ones require their own hardware and are too expensive for individuals.
Blender has its own compositor which is getting better with each version.
For motion graphics work like Adobe After Effects or Autodesk Combustion, there are very few options; either ZS4 or Jahshaka.