When I saw this tread, I immediately thought of this plug-in:
http://www.alexhilton.net/A1AUDIO/in.../a1triggergate
It's a gate/sequencer. Very nice UI and it has some very nice presets. Four of them are sidechain emulations. Combine it with using the attack, hold, decay, sustain, release and mix knob..you can get very nice and different types of sidechain sounds out of it.
The Vst follows the tempo of your project and you can draw in the sequence pattern yourself if you prefer that.
By the way, it's free. Which is crazy considering it's such a quality plugin.