There are SHYTELOADS of vsts out there. As with anything associated with what we do as recording/mixing/mastering engineers/beatmakers, only trial will inform you as to what is "good" or "bad". Someone's favorite compressor might be someone else's garbage.
Google "free vsts" and begin your search.
If you're using PT, however, you will need to get your hands on a copy of FXpansion's VST to RTAS adapter. It's $100US, but it's worth every cent you spend on it. It's stupid easy to use.
Have fun. VSTs never stop coming out or getting updated.