D16 Devastor 2 - Clean downsampler and retro sampler emulator, which also turned out to work as an outstanding exciter and aliasing stopper (probably more than just a simple LP filter).
Kazrog True Iron - Nice but subtle transformer-based saturator with easily switchable 6 modes, at least one of these does something to a signal.
Wavesfactory Quantum - Streamlined transient shaper with a number of onboard effects that can be applied to either transient or sustain part of the signal. However, I don't use these. I just use Quantum as a transparent transient splitter for further processing with my tools of choice. Yep, I paid 99 USD just for this utility
iZotope Breaktweaker - Popular sequencer and sample mangler that hopefully will help me to create wild drum loops, rolls, breaks and effects. For 9.99 USD it's a no-brainer.
So overall a bunch of mixing tools and effects that will help me get the most of synths that I already have.