What I use in addition to most of the things listed above, I use almost all of Netherwork's scripts:

Batch Material Convert - Converts legacy .pz2 mats to .mc6s and moves them to the Materials folder (where Material files belong).

Creator's Toybox - very useful in unscrewing content I have purchased both here and elsewhere.  Especially PROPS!

Hair Conversion System 2014 - converts M4/V4 hair to something Alyson 2, Antonia, Dawn, Jessi, Michelle, Miki 3/4, & Roxie can use.

Hair Conversion System II (and a copy of Poser 7) - Converts M4/4 hair to something James, Kelvin, Koji, Simon, G2 Jessi, Sydney, Olivia, Miki 1/2 & Terai Yuki 2 can use.  One day, I hope Netherworks will update the figure data modules for use with HCS 2014, so I can retire my copy of Poser 7. (Hint, Hint)

PoseWriter - for reworking M4/V4 poses for other figures.

By Semidieu:

Advanced Figure Randomizer and INJ Builder - essential for figure clean-up.  (Reduce that 400Mb V4 to 20Mb)  It also builds Inj/Rem files

Advanced Texture Variation - when I need something other than the generic Caucasians that litter the Poserverse.  Really lets me add variety to skin textures

By 3d Universe:

Texture Converter 2 - Allows me to put M4/V4 textures on the Daz Generation 2 & 3 figures as well as Miki 2.  Pity 3d Universe dropped the product.

By Blacksmith3d

Texture Transformer - Allows me to put V4 Textures on Roxie & Dawn - Hopefully, we will see support for more than just DAZ figures.