(Time to pull a rabbit out of my hat.)
(23 is the answer to everything.)
I did a quick count of the last few projects and found I am using about 15 regularly.
I figger dudes who are working with audio more than me prolly use about 2 times as many.
And, as THE CRAIG has written, nearly all the plugs we have had for years do much more than at first seems.
So, my suggestion is to learn how to do more with less, and hence save the life-time of searching for hours to get stuff, and then spending lots of hours attempting to learn them, and then maintaining them, and then abandoning just when the learning has begun.
I have purchased 3rd party plugins such as Kantos, and Ozone (still v.3), and VSampler 3, and various samples, and other bits I gathered along the journey. But I mostly use the stuff included with Sonar 1-X3: DP, SD, Rapture, Zeta, Sonitus EQ, reverb, modulator, gate, compressor, Perfect Space, Boost, and CW Amp Sim (a lot). I have Guitar rig in a few projects, but not for guitar. Most of the guitar is recorded from the amps.
No doubt Breverb, and AD, and Overloud, and all the new plugs from the last 3 Sonar versions are great. But I have limited time. If I can get more from Sonitus Reverb then I have spent less time and know more.
(My favorite big reverb is PS with a forest impulse, followed by PS with a canyon, cave, or cooling tower impulse.)
What I have read in the Sonar forums for the past 12+ years is the included plugins, effects, and synths, can do just about everything most of us need.
No doubt Waves, and UA, etc are great. And no doubt some of you guys have them.
But, how many individual plugins do you use regularly?