Massive and FM8 of course, the Kontakt libraries (Factory, Vintage Organs, the Pianos and the basses and the possibilities of expansion), Reaktor is fun, but difficult. And Guitar Rig has some of the nicest sounding compressors IMO. They are so broad, that they enabled me to experiment more, instead of being limited to a certain style
But I'm still at version 8, so I can't say anything about newer additions