I already have the Virus and several other VA gems to provide that kind of sound texture, and therefore I tend to look for the exact opposite in a soft synth, namely digital, sample-based, huge ability to manipulate the sound and integrate it with sources of a different nature.
I totally agree with TheHobbit's suggestion for the Kore Player, but I would go even further and suggest buying the whole Kore 2 package, including the hardware controller (you can find the combo for about $300 from NovaMusik and other discount retailers), which gives you excellent real-time tweaking abilities, even in a live setting. Besides, it's so cool in its brushed metal/black matte plastic finish and red LCD display that it looks like one of those marvelously designed but outrageously expensive Bang Olufsen pieces of stereo equipment. Also, if you own NI's Komplete (which is another package I heartily recommend) or even only parts of it (Kontakt, Absynth etc.), Kore will provide such a degree of integration you won't find anywhere else. Not to mention the ability to look for sounds in a single tightly-integrated database searchable by keywords (yep, our problem today is that we have tens of thousands of patches to sort through and not merely a few hundreds, like when the whole MIDI thing started in the early eighties.) Let's not forget that NI also provides reasonably-priced add-ons for Kore (also usable with the free Kore Player), some of which (like Evolve Mutations 1 and 2) are true gems that will knock your socks off. Also, having professionally grown in the eighties with the legendary DX7, I find NI's FM8 VSTi indispensable (yes, I can still use the same sounds I programmed when I was a quarter of a century younger!!)
http://www.native-instruments.com/#/...?category=1302
I can say that most of my soft synth sounds come from Komplete and Kore, including lots of add-ons for both, either from NI or third parties.
Outside of NI's plugins, my recommendations include:
Alchemy. Definitely fun to play with and easy to program. A very unique and distinctive sound engine.
http://www.camelaudio.com/Alchemy.php
Omnisphere. Yeah, I know it's expensive, but IMHO it's worth every penny:
http://www.spectrasonics.net/instruments/omnisphere.php
H.G. Fortune's quirky creations. If you're into highly unusual, dreamy, odd, spacey, randomly-generated sound textures, look no further than his range of very reasonably priced soft synths.
http://www.hgf-synthesizer.de/
Rob Papen's Blue and Albino:
http://www.robpapen.com/
Big Tick Audio's Rhino:
http://www.bigtickaudio.com/bigtick/home
AAS's Tassman 4:
http://www.applied-acoustics.com/tassman/overview/
LinPlugs' Octopus:
http://www.linplug.com/Instruments/Octopus/octopus.htm
LinPlug's Sophistry:
http://www.linplug.com/Instruments/S.../sophistry.htm