I don't like topics like this one. In my opinion it is all about the idea, about melody, about composition, not about synths. I heard a lot of different music styles created only with IL Sytrus VSTi from dance/trance, via Hip Hop, up to Funk or Jazz. Everything is up to you and how you will use the VST.

TB303
Novation Bass Station

If you're going for 90s dance sound, the best synths are sample from 80s records

Purity reminds me of the sound of a Triton/Trinity. I would start there.

I listened to rock in the 90's, so here's a hmm with 31 m's.

hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

I thing the original post is far too vague. I mean, give us something to go on at least? Are you asking for a list of synths released in the 90's? There were many models that came out in the space of ten years. Do you mean synths that were used in the 90's? Ih that case, you need to add everything released in the 70's and 80's. Do you mean a particular style of music? It might help to let us know what that style is. Are there particular signature sounds you're after? If so, why not provide a song for reference?

In other words, if you want a useful response, perhaps you should put a little more effort into your question. Just my two cents...

Every synth will do, I think. I searched for the oldschool house sounds and found them here:

http://www.dancemidisamples.com/DMS-Rave-Samples.html

But that depends on what you call ninetees.