Oh god. The question I dread. At least I'm in good company here - I'm sure I'm not the only one who has picked up dozens of things over the years because they just seemed like deals too good to pass up, and good stuff that I *could* find uses for... but in reality, I probably own licenses for about 10 times as many things as I actually use on a regular basis. 
 
Well, soft synths I do tend to use a lot so I'm not too red-faced about that. Most things in the Arturia bundle and Komplete, as well as stuff from AAS get called on quite a bit, as do sample libraries from Sonicouture and a handful of others. And Alchemy - still gets used even though it will never be updated again unless I move to Macland, which is not happening in the foreseeable future. I have an on-again-off-again relationship with the IK stuff (Sampletank and its vaious appendages) as well - sometimes it seems to be just what I need, other times I don't find myself reaching for it. Having said that since I go through frequent periods where I'm not producing much as my time is dominated by performance (and family) duties, there are a few synths and libraries that have fallen through the cracks as well - Synthmaster, the AIR stuff... maybe this year...
 
FX is even worse. I have used some of the CW stuff a lot - I don't often find myself needing outboard EQ when the Quad is so flexible and right there... so why do I have 200 other options? Same for compression - half the time I stick CA-2A on there and make a few adjustments and it's pretty darn close to what I want. Maybe Supercharger if I want something more heavy-handed. I'm not actually a particularly fussy mixer, truth be told, so why do I need all this other stuff? Just because it's on sale and probably great doesn't mean I need to own a license. 
 
I tend to be more motivated by 'out-there' FX, so things like Molekular get used a lot, and a little overlooked gem from Audio Damage called Automaton. I also have done a lot with NI Kore which, like Alchemy, is still installed here and gets used despite its tragic discontinuation. 
 
I have Ozone (advanced, came with the MPB2) for mastering, though that's relatively recent so more of my stuff has gone through T-Racks over the years - I got a lot of mileage out of the Fairchild and Pultec plugs, and the Brickwall was my go-to limiter for ages as well. I wonder if I will miss it now that Ozone gets first call. 
 
So yeah, I'm going through a bit of a soul-searching thing on why I need to have all this stuff I don't really use... it's so easy to justify when the sales are on, and it only takes hard-drive space, it's not like I'm physically tripping over it on my way to get more coffee... no, that's the mandolin, or maybe the flugelhorn... 

softsynths, disco-dsp discovery pro and u-he diva are my usual gotos, with zebra2 and synthmaster close behind

Afrodrum
Sonar has every time fx, mixing and basic mastering plugin I need. Exception is Waves L3 I use frequently on master bus. I only buy amps (full TH3, got Amplitube 3 too but don't think I need to upgrade to AT4 yet), VST instruments, and modulation effects. Later I realized that except for PSP Lotary and PSP Scanner I would be well with just Sonar FXs. Seems I was weak at fighting GAS.

Oh yeah, L'otary and B-Scanner. Just picked them up for a song on special and have already used them a couple of times. Simply amazing! Realism on a kind of scary level. 

Oh yes and universal audio la-2a and 1176. I like the universal audio pretty well but seems like I whined up using other plugs.
WSS