Like it's already been stated multiple times if you're interested pick up Komplete
It has like literally everything, and even if you're not going to be using half the things I'd suggest picking it up (basically it's like getting just about everything for the price of just under 2 of their flagship plugins) - it comes with so much content.
I picked it up a few months ago and I still haven't explored everything to the fullest, I was mainly interested in getting a few of the synths but I've found myself using Kontakt more than anything else.
As for NI as a whole they're products are all rather high quality, though some may be a bit overboard on the price, but getting Komplete kinda destroys that anyways.
Kontakt - if your orchestral sounds atm suck it's definitely an improvement, but honestly I'd look into investing in some better libraries for that sort of thing to use in Kontakt, the sampler's great but the factory library isn't all the most impressive - definitely passable but it's not like amazing, you're mainly paying for the sampler here. It has a free version but it kinda limits which libraries you can use in it, I've noticed most are actually limited more with the cheaper libraries (the more experimental ones) less than the big omgamazing quality ones - I'd look into this site for some libraries if you do pick it up:
http://www.soundiron.com/Massive - honestly?
I think it's overrated
It's a good synth but it's not like the penultimate electro synth, be prepared to do a lot of post processing to clean up things you make in it if you want to make the dirty electro sounds, really it's main strength there is it's performer Envelope controller. This thing gives you massive control over envelopes to just about everything so you can craft some really intricate sounds out of it if you mess with it enough.
FM8 - aaaaaaaaaaaaaaaa how does this even work these presets don't show me all that much I'm not impressed but messing with it this thing is really powerful now if only I could figure out how it works.
FM8 will get you some massive impressive sounds if you know how to use it, but that being said it's FM synthesis and FM synthesis can take a bit of work figuring out, not as bad as additive but it's still a bit complicated. Definitely rewarding though if you can figure it out, and like I said most of the presets don't really show it's capabilities much at all.
Absynth - honestly I had considered it like THE trance synth for a while
http://www.youtube.com/watch?v=tsOppMF_7p0 - and then I saw this
I hadn't really explored it much but it's got a shit ton of synthesis options to it, this is probably the deepest synth NI offers.
Battery - :I
The built in sounds suck, most of the drum kits would take quite a bit of work to get many good sounds out of - some of them are neat but honestly I think I'm missing the focus here if I'm paying to much attention to the sounds themselves.
For a drum sampler it's pretty powerful, and not to mention pretty CPU light too so it's easy to just through sounds in if I want to edit the drums easily or get velocity control on something that's just a 1 shot sample.
I personally wouldn't buy it on it's own since most of what it does can be done manually, but getting it on Komplete I'm not complaining.
Reaktor:
Forewarning - anything in this eats up double the CPU similar standalone plugin would.
That being said it's a powerful synth construction platform..... if you don't mind the extra PC load, I wish I knew how to work it better.
--Spark - ......they're charging money for this? Jeeze I'd just include this in the factory bundle the only reason I even have it is Komplete and I've never been very enticed to explore it much since it just seems like a glorified subtractive synth, not very special in tone heck a ton of the sounds you can get out of Carbon 2 which comes with the free version of reaktor.
--Razor - fat juicy basses, razor sharp leads and some awesome format and vowel filter controls....... and it eats up CPU like none other, it has to be the most CPU intense plugin I have which sucks really because I love the tones it makes, just putting one in my tracks makes my program like 10 times glitchier so I have to resample it all the time to make it usable.
--Prism - have my babies this is like my dream synthesizer
Well really it's an awesome acoustic modelling synth so don't expect much usable in like any generic genre but if you like surreal bell and string tones it's great. The free version Mikro Prism is nice in it's own right too and can pretty competantly hit most things I've gotten in the full version so if you're not getting Komplete I'd just pick up the freeby and be done with it.
--Other stuff the full version comes with - it has a ton of synths, many of which I haven't fully messed with but it's loaded with plenty of things on hand (probably like around 20 or so synths and effects). Most of the sounds aren't all that special but they're definitely usable, more than just the average free plugin. I do really like Green Matrix which gets some pretty nice Acid sounding synths.
--Guitar Rig - it has some pretty sweet effects in it. That being said I haven't explored it all that much and unless you're doing like a ton of guitar work you'll find most everything you need in the free version.
--Traktor - an effects collection for Guitar Rig that came with Komplete
Honestly I don't find much of it useful to the point I'd use it over the native effects for Pro Tools, I use the overdrive every now and then but most of the effects don't strike me as anything all that special, I wouldn't buy it on it's own.
Hope this helps!