If you already have a host program, then just search google for vst programs and look for something that suits your needs.

I would suggest getting Reason 4.0 but that is not free by anymeans. Also items like Kore and other programs would work well. You should have a look at an online music store and browse around to get a feel for what you would like to download, then go look for free software. (mind you I dont mean stolen)