3dsmax - Discreet

Afterworks
The creator of Afterburn and other fine tools

Image Lounge
A great plugin set for After Effects, includes focal blur tools.

Orbaz
Oleg Bayborodin, The creator of 3dsmax's Paerticle Flow, Particle Studio, and Sandblaster is creating special updates for Particle Studio. Very nice particle tools.

Turbosquid
3d tool distributor.

Frischluft
Really great After Effects Plugins, I use them all the time.

Final Render
Excellent and relatively inexpensive rendering plugin for 3dsmax