As recently discussed in another thread here, the upgrade of AAS String Studio to V2 has caused me to reevaluate it.  A new demo video that was released to accompany the new version made me see what I had previously been overlooking - a lot as it turns out.  That doesn't make SS a top-five synth, but it does make it one I'll give a lot more consideration in the future.
 
And then there's Massive.  Never thought too much of Massive before, but I recently watched an excellent Groove 3 video series on it, and there's much there I'd like to dig in and experiment with.  Massive might end up in contention for a top-five designation before this is all over.

Kramer Tape, but I've just bought J-37 which will work even better on some things.
IK's Faichild and Pultec.
Waves L1.
 
But more than anything else, what I've come to realize recently is that in most cases, I'd rather spend my money to get the sound I want in front of the converters instead of in the box. I could spend $5000 on EQ plug-ins and not be as happy with my sound as using a simple outboard EQ such as an inexpensive DBX or even that on a little $100 Mackie mixer. I believe transparent processing upfront can do a lot more for my mixes than tons of esoteric virtual analog processors ITB.
 
As for the rest, the bundled plugins in my DAW are more than adequate.

I must say I just fall in love with Geist more and more the longer I use it. Not a perfect piece of software but it comes close. Nor is it a drum solution for every song or genre. But as a drum machine/sampler/beat slicer it is an absolute joy to use. Once you figure out the workflow for chopping a 4 bar or 8 bar drum pattern out of a drum track (I use Sonar to chop the ballpark loop out) and import it into Geist's slicer, it's so quick and easy to get everything sliced, loaded into the pads and mangled. And I've yet to find any need to multi-output the pads because the onboard effects are awesome. In fact with the inbuilt pattern sequencer and song arranger it's pretty much possible to put entire tunes together without ever leaving it.

Using the interface is a pleasure and this is one of the rare cases in which I'd give 10/10 for a manual (it makes the Melda manuals look like gobbledygook in comparison). Worth every penny, Geist is (especially if you manage to pick it up in a sale).

Mautodynamiceq .That is all

cclarry
The Maag is clean as clean and can put a sheen on your mix machine...
It has great character, and the Air Band, for adding "air" at the top...
unparalleled IMO...it's a monster...

Want a taste...try this one...it's a Clone of the Maag, nice, but not quite
as good...

It's freeware...check out the video...

http://myvst.com/vst-effects/luftikus-freeware

 
Larry! You rock pal! Thanks!

iZotope's Alloy 2.   It's a combo effect, but that's one of the reasons it works so well.  And, you can activate or deactivate any parts of it to have more or less of the stuff in play.  Really great on tracks, and then after you freeze a track it has no hit on the CPU.
 
Example, let's say I have an acoustic guitar track.  I can fiddle with all sorts of independent effects or ProChannel effects (which I do).  I seem to hit the right spot super quickly by adding Alloy 2 to the ProChannel (as an effect in an FX Chain in the ProChannel).  I can pick an acoustic guitar preset and whammo! it sounds great.  I can tweak from there, and / or add other effects as desired.
 
I think it's a really nice tool to have in your arsenal.

bitflipper
There is one plugin that just keeps amazing me anew every time I use it. I could tell you what it is, but it's my secret weapon and I'd rather take undeserved credit for my mixing abilities than admit the truth.

ARC 2?

Let's see.
 
1. Ozone 5 or Slate FG-X (it's one or the other depending on the style of music)
2. Lexicon LXP (hoping to have the PCM bundle some day)
3. Fab Filter Pro-L
4. EZDrummer
5. UAD's Helios or Harrison EQ (it's one or the other depending on the instrument)
6. Native Instruments KONTAKT 5 with either Passion Flute, Kirk Hunter Strings, Action Strings, The Giant... too many to list actually
7.Waves ADT, J37 Schepps EQ.... too many to list also
8.........
 
 

No question for me - the Quad Curve EQ is in everything I do. 
 
After that, Kontakt has become the one plugin most likely to make an appearance is just about every project.
 

bapu

bitflipper
There is one plugin that just keeps amazing me anew every time I use it. I could tell you what it is, but it's my secret weapon and I'd rather take undeserved credit for my mixing abilities than admit the truth.

ARC 2?

Close. It's the one I PM'd you about a couple months ago. I wanted to make sure I wasn't hallucinating. You assured me that I was, because you didn't have it and therefore it must not exist. I could have brushed that off, had not yorolpal given me the same opinion.