go to the KVR website, there are literally thousands of free vsts...
make a folder in your VST folder for plugins you havent tried yet or you'll find yourself swamped with them or not remember which ones you've tried...that way if its crap you can delete it, if its good you can move it to the main folder
there are some very good freebies out there like Kjaerhus Audio and digitalfishphones, look them up...also de la mancha has some very good vintage plugins which can add colour for ridiculously low prices..
I think eventually its good to pay for a handful of really good plugins, a decent compressor and/or limiter is likely to be needed, but there is plenty of good freeware out there
Another great source in Computer Music magazine...its expensive at $15 but it comes with a DVD every month that has a huge library of effects and vst instruments..if you coincide buying it with a feature in the mag thats interesting to you then its a win/win. It also comes with a series of basic tutorials for beginners on the disc as well. happy hunting