While I'm taking a turn farther toward game design on this blog, I still haven't quit music. Today I want to recommend a great free VSTi, especially in the neighborhood of Drum and Bass or Dubstep.
Kairatune came out this year, 2011, and is the perfect solution for those of you who want a strong monophonic synth. I've added it to my VST collection quite happily. Here's a good demo, which still only shows a chip of what's possible with this synth.
Kairatune Demo by Kairatune
Most of the knobs don't turn properly, probably due to a bug. But I found a workaround by using LMMS's VST parameter converter to set the knobs.