Crystal VST
Been around for some time. Quite well respected. Free. If I knew how to post an image I would, but go to the site to see.
http://www.greenoak.com/crystal/about.html
From the About Page:
What's Crystal?
Crystal is a semi-modular software synthesizer featuring both subtractive synthesis and frequency modulation (FM) synthesis. It offers abundant modulation control with over 90 parameters which may be modulated, multi-stage envelopes with graphical editors, extensive tempo sync of envelopes/lforates/delay times, built-in effects for chorus/flanging/comb filtering/echoes, and a band splitter for effects processing by frequency band. Not only that, Crystal has wave sequencing, granular synthesis, program morphing, MIDI learn, and imports soundfonts. The musical applications for Crystal are literally boundless.
Crystal is a plugin, which means it runs within a host, such as Cubase, Orion, Logic, Fruity Loops, etc.
Listen to examples of what kinds of music people are making with Crystal by visiting the Demos page using the link at the top of this page.