It is indeed highly subjective, so here is my personal list of must haves:

**Advanced Figure Manager by Semidieu
**Essential for working with complex scenes containing many figures and props

**VSS by Bagginsbill
**Free utility for applying shaders to multiple material zones

**Morphing Clothes by Dimension3D
**For transferring figure morphs to clothing, making clothing much more versatile

 

*** Others I find very useful, but not essential ***

 

**Advanced Material Manager by Semidieu
**Powerful tool for working with materials

Advanced Render Settings by Semidieu
Especially useful if you want to postwork your renders

PoseMorphLoader by ColorCurvature
Hard to describe in a few words, but a fantastic tool if you have some basic modelling skills.

**Snarlygribbly Snow machine
**For making Winter scenes

**Pose2Lux
For exporting Poser scenes to Luxrender
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Free stuff @ https://poser.cobrablade.net/