Uniretro by by Christoph Bielen is a nice free VST synth for all your trance sound needs.
Here’s more details (quote from Synthmaker/Uniretro website):
Uniretro is an excellent virtual analog synth capable of impressive trance sounds thanks to the innovative sequencing and retrigger capabilities.
- 3 x Multi-mode oscillators with PM and FM capabilities
- 2 x User Envelopes
- 2 x LFO
- 1 x Multimode filter
- Pitch, Trigger, Hold and Modulation sequencers
- Distortion, Decimator, Chorus and Delay effects
- 50 Presets
- Up to 4 Voices
Check the video for some sound examples: