MDrummer offers VST plugin and standalone versions. MDrummer S is a free MDrummer edition which contains everything you need - standalone application and VST plugin.
MDrummer freeware versions has just been released. Release of the commercial editions of MDrummer is scheduled for the may 2008.
MDrummer DEMO Download
MDrummer demoversion is definitely the first thing you should try. It shows all features, however it cannot save or export anything, generates random noise and contains only a few resources. However you can setup your own drumsets and rhythms and even use the rhythm generator.