My wife...
 
Stops me in my tracks before I even get a chance to fire up the plastic. She has a god given sense of intuition about when I'm going to buy something.
 
"Hoarding again?"  I jump through the roof startled about to death. Thought I was about to do a clandestine purchase and blame it on car repairs. Didn't know she was right behind me.
 
Argiung that I really really need EQ Macho Blaster, and 99% off for one day only.
 
Pretty brown eyes throwing flames at me. Busted big time.
 
I usually retreat back after my hot flash subsides and see if there is something I already have that will do the job. Most of the time, there always is.
 
John

Arc 2. Hearing things 'correctly' has helped more than anything else...after that.
EZ Drummer 2
S-Gear/Amplitube/Mark Bass Studio
Everything from Tokyo Dawn, Valhalla, and Klanghelm
Pro-Q, Mautodynamiceq, LimiterNo.6
Melodyne Studio...Duh!

Cakewalk's Sonitus fx:Reverb. I don't use it on finished tracks (right now I tend to use NI's RC48, Waves IR-1 or, IKMultimedia's Hall reverb for final mixes), but when I create sketches and test compositions, I use Sonitus as a quick and easy-to-run reverb. So, while it's not a finishing tool, its involved at some point in pretty much everything I do. And for an older plug, it still sounds perfectly decent.

#1 on my list is the TB-4
 

 
And if that doesn't work, I follow it up with some T-P.
 

Fleer
No love for Arousor?

 
I demoed it and loved it, but not $300 - $350 loved it.
 
Equick possibly my most used. Shout outs to MJUC and Slate VMR though.
 
 
 

Besides EQ and compression, I think that the plug-in I use the most is called "Direction Mixer". It's especially useful with virtual instruments and drum libraries which tend to be all over the stereo field - such a plug-in allows one to manage that. I also use it on busses with reverb.
 

 
I'm guessing that Sonar has something similar (which I am anxious to find out for myself the minute the OSX version is released!)

arachnaut
I think I use Reaktor every day.
 

I'll second NI Reaktor.  I've got like 10 instances of Reaktor in my favorite template.  Compression, effects, drum machine, synth.  

Rain, where do you keep finding these beauties. I'm thinking you read the manuals.

Fleer
Rain, where do you keep finding these beauties. I'm thinking you read the manuals.

When I switched platforms in 2010, I decided to do everything I could to ease the transition to my new DAW. These helped speed up my workflow quite a bit. ;)
 

David Dvorin. Got it. Now to read it. Damn.