Hey guys, apart from the Cubase compressor and Pro-C by Fabfilter, we really haven’t had many choices for VST3 compressors.
But a really awesome compressor just got released by DMG Audio which is VST3 compatible (including 64 bit support too). http://dmgaudio.com/
I’ve tested this compressor in Cubase 6 and it works perfectly for sidechaining and just about all compression duties I had used my previous compressors (GPP-1, Marquis and Sonalksis) for.
What do you think about it? 
Be sure to also check out EQuality while you are at it, it’s also VST3 compatible and is also awesome!