As for effects...
 
https://www.native-instruments.com/en/products/komplete/effects/molekular/
 
A lot of the demos on their site are for EDM things, and it works fine for that, but it excels at ambient transformations as well.  I wouldn't be exaggerating too much if I said that you could put Limp Bizkit into it and get spa music out.
 

Thanks Magic Russ for the link to Homegrown sounds for Iris. The free ones are excellent as are the Dark landscapes as well. 

Oh and for occide here is another one. Native Instruments Prism. Now there is a serious synth with some very serious pads and very organic ones. This synth cam move its harmonics by modulation both horizontally on the spectrum as well as vertically of course. You won't find anything that sounds like it.
 
Also Yamaha SY77. (hardware) This has got some very serious pads too. Harder to come by but stunning none the less.  I believe the latest Montage 7 has the biggest and best FM engine of all time built into it too. FM7/8 can do these sounds too.  I have got a massive DX7 library and some real killer organic pads too. They sound amazing on the TX816 which is effectively 8 x DX7's. But FM7/8 can do it with its unison mode. Just select 8 or 16 unison voices and detune them slightly and behold.
 
Samplers should not be left out too. You can record interesting things and really mangle the recordings. Pitch them way down, reverse, effect etc.. Here is something I discovered by accident one day. Take some canned laughter about 2 to 3 seconds in length. Not too funny just a medium style laugh of about 50 or 80 people. Easy to find. Pitch this down about 24 to 36 or even 48 semitones and play it. (pitch and time now e.g. old school) You will be shocked. Sounds like a small spacecraft is hovering very close to a huge mothership while the massive mothership cruises slowly past.  You can hear warp drives in slow motion, creeping sounds and metallic bangs and things. I nearly fell over when I heard this.  Add some reverb and revel in this. I was only attempting to pitch some laughter down -1 or -2 semitones for a comedy play but entered the wrong value by mistake. I was shocked. If a director asked me to make this effect I would need 5 hours and about 20 tracks to do it. But the laughter pitched right down sort of nails it in a flash. Who would think!

That reminds me of a track I did back in the SoundBlaster days.  My bass line came from a shakuhachi patch that I played about an octave lower than the lowest sample.  Since older samples stretch pitch by adjusting sample length, my bass line turned into this long drone that only vaguely sounded like a shakuhachi.

occide
 
So I bought Iris 2 now

Iris 2 has a truckload of content that is not available in the demo version (quick reminder if you haven't looked at that yet), and a couple nice features of it is the spectral masking and how their modulation matrix is set up. In some ways this is not intuitive, so watching a few videos on those specific items will shed some light on things.
 
When I first demo'd Iris 2 was during a promo for 4 things from iZotope, my first pass on it was "meh" but I came back to it for a more in-depth look and realized what it is capable of. Once you get a handle on the spectral masking, it can do some very interesting manipulations to almost any sample (i.e., you can make a lot of things which are not "organic" sound like they are). Adjustments to the sample area, spectral content, how it is played (forward, backward, oscillting, etc.), and root note are just a few things that can be done with the sample itself, let alone layering it and the modulations available.

Have you taken a look at Rapture (classic) yet?  The Expansion Packs 1 & 2 are not to be overlooked.
 
Lots of cool ambient presets in the Film Textures & FX, and Pads categories in both packs! 

Great, the forum swallowed my previous answer. :(
--
And it did it again.
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So the problem I have with "dated" is not that a software is old (but still gold). I recently bought the "Air Complete Collection" and a Sonivox Plugin, both are full of bugs. Digging the web I found that these bugs have existed for more than 2 years, and that both Sonivox and Air are pretty much out-of-business / sold. So nobody is ever gonna fix that code. I basically threw money into the sewer. That's why I'm looking mainly for recent plugins. "Dated" means for me "potentially no longer developed / supported".

I've got an eye on The Mangle but only because it's cheaper than Granite. Otherwise I'd go for Granite if it was around 50€.

Some great recommendations by you guys, definitely gonna check out all of them!

Yesterday I tried to follow the idea of spicing up a traditional synthetic synth with a granulator and reverb. I went through this list:
(seems I'm not allowed to post links anymore. Dont ask me why)

But most weren't very good. Argotlunar would be the best imo.
 
Then I played half of the day with MMultibandGranular - definitely an awesome plugin but I was unable to get the results I imagined, like making a traditional synth sound more natural. Not sure in which direction to look next. I'll definitely favour an effects plugin over buying one instrument after the other.

The best free reverb I could find for my cause is OrilRiver:
(seems I'm not allowed to post links anymore. Dont ask me why)
 
 

abacab
Have you taken a look at Rapture (classic) yet?  The Expansion Packs 1 & 2 are not to be overlooked.
 
Lots of cool ambient presets in the Film Textures & FX, and Pads categories in both packs! 

Funny thing, I was going to mention that.  I have been on a tear lately making presets for that synth.

Magic Russ

abacab
Have you taken a look at Rapture (classic) yet?  The Expansion Packs 1 & 2 are not to be overlooked.
 
Lots of cool ambient presets in the Film Textures & FX, and Pads categories in both packs! 

Funny thing, I was going to mention that.  I have been on a tear lately making presets for that synth.

It's a fantastic synth, but some of the stock presets did not really show what that synth is capable of.  The Expansion Packs are a different story!  I get lost every time I start looking in there, and don't get much else done, LOL! 
 
Never tried any of the 3rd party expansions, but I did grab the free Muz3uM for Rapture. 
http://patcharena.com/syn...rces/cakewalk-rapture/

occide
Anything like Blackhole? Not more than 50€? :|

Here ya go. Fifty bucks.