For trance, and for any other type of electronic music really, I will always suggest you learn how to synthesize your own sounds. Instead of relying on there being someone out there who has made the exact sound that would fit into your particular track.
So you go out and buy huge preset banks and romplers like nexus and omnisphere, after having used all the sounds that you like you find yourself wanting other sounds so you go out and get even more sounds and presets or whatever, and then the story goes on indefinitely.
Every great sound you hear in those big banks of randomness, someone synthesized them, and you could to if you would just take the time to learn how to do it. Once you master that, your preset searching days are over and you can actually imagine the types of sounds you want and can picture how they would be done and implemented in your tracks instead.
If you're looking for sample libraries with recorded analog instruments, guitars and violins and whatever it may be, I can fully understand Kontakt and it's excellent sounds.
But when you want to make music that relies heavily on synthesis and quirky unnatural sounds, I just can't for the life of me understand why anyone would ever want to go and waste their money on something that a couple of well selected vst synths can do 100 times over, plus change.
Damn you people, why won't you synthesize!!?
You can't just learn how to play the keyboard and get really good at that like you would if you were going for career in piano or guitar playing and then leave it at that. You have to create and design your sounds if you want to make trance. The whole point with it is to play with synthesisers and make the whole universe vibrate. Learn how to play your damn instrument.
Just had to get that out of me, sorry I was of no relevant use to this topic.