XSIGradient
XSIRuleOfThirdsThis allows the user to set a gradient background within the Softimage Viewport.
XSIEnvelopeThis plug-in allows the user to see a 'tic-tac-toe' grid over their camera.
XSISelectionSetsThis is a suite of tools aimed at making the enveloping process a bit easier.
PoseBallsA quick and convienent way to store and access selections.
Downloads for x32 & x64 and a slightly longer description can be found hereThe benefit of this plugin is that it allows you to create persitant pivots for scenarios where you will want to rotate an object around a static pivot in relation to itself.