I think I use Reaktor every day.
 

Gotta throw some love towards Slate too. His VMR is getting better and better, now including those famous bluey 1176 compressors.

I'm diggin' the VMR as well but ARC and Sonarworks are indispensable here.
 
Rocky

SONAR's own QuadCurve EQ.    I haven't had a single project without it since first introduced.
 

1. QL Spaces
2. FabFilter ProQ2
3. FabFilter L
 
I use them on every single project.

CW's CA-2A, Arc 2, and Wave's L1 limiter.

No love for Arousor?

A year ago I would have said Arc 2, but not Sonarworks for sure. 
 
I also use HornetVU meter on every project. However, once I use it on each track to figure out the trim adjustment I make the adjustment in Sonar and delete the plugin.
 
EDIT: BFD3 and Stylus are in every project I do. I was thinking only effects and not instruments. duh. :)
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I also seem to reach for the UAD Pultec and UAD 1176 a lot. And the UAD Ampex on the master buss almost always. And the UAD Fairchild on drums most of the time.

Audified MixChecker.

My most used plug-in is probably my most boring. And it is only the most used because I have it inserted as part of default track template.
 
Breverb 2
 
I'll get me coat...