Cannot get enough softsynths, it's a problem because I spend a lot more time sound designing than I do actually making songs. I'm basically forcing myself not to make any more synth purchases until I get something done

. I really want to make a gigantic preset pack and put it up here at some point.
I suppose I'll contribute and do some quick two sentence reviews:
Massive - The obvious go to for bass music, and rightfully so given its amazing modulation and effects section. Filters are kinda shit though, so it doesn't handle VA duties as well as Sylenth or Zebra does. Not to say that it's only for wubwubshit, ofc.
FM8 - Not quite as familiar with this one as I am with the others, but it's very nice in my experience even for non-FM duties (surprisingly good supersaws, for example). The major downside is that FM has a steep learning curve, which can make this one difficult to get into if you don't make an active effort to learn.
Absynth - I have hardly touched this thing at all as it's very weird, though it's one of many many things that came with Komplete so I'm not complaining. As far as I can tell it would be great for pads and atmospheres, and it's got an included effects version so it could also be useful as a "fuck shit up" machine.
Sylenth1 - The most recent purchase I've made, after resisting for years due to the developer being a hermit. Cannot believe how good this things sounds, almost completely makes up for the lacking modulation section and weird filter routing (which I suppose is part of the reason why CPU usage is so low).
U-he Zebra - Softsynth perfection, flexible as hell and sounds amazing to boot. Not quite as fast to get usable results as Sylenth in my experience though, and it takes a bit of tweaking to get "that" sound. On another note, I think that
this skin may be relevant
Camel Alchemy - Sample mangling monster, this thing will take whatever you throw in and spit out something completely different if you so desire. Also capable of standard VA work, though it'd be a waste to use it just for that. Also, it includes all of the effects from CamelPhat and CamelSpace, so needless to say it's quite good in that department.
Z3ta+ 2 - Picked this one up for super cheap during a Christmas sale, and goddamn what a value that was. Scrolling through the preset library is an instant indication that this is basically made for EDM, through and through.
Oh also freeware
Synth1 - The definitive freeware synth.
DUNE-BE - A completely free version of DUNE, a synth that people often compare to Sylenth for its huge sound. The only missing features are the effects section and 64 bit support, making this a must-have.
Tyrell-N6 - A freebee from the creator of Zebra, sounds amazing but hogs CPU like nothing else. Really requires the
Tyrell 1978 skin to look its best.