Hammerhead's good.
Here's a
LINK to it in case you don't have it yet...
Do a search @
KVR Audio. It's kind of tricky to search the site, but I'll give you the basics.
First, when you click the link about there will be a page with a column of options down the far left hand side of the page. Skip the first 2 ('Receptor' and 'News') and click the one that says 'Instruments, Effects, Hosts, Etc.' That will take you to a 'Database Query' page and if you scroll down you will see that there's lots of choices beneath the fold.
In order - 1a is 'general plugin/host type' --- choose 'instrument'.
1b is 'choose specific plugin/host type' --- be sure to uncheck 'all', then check as many as you want to come up in your search.
2a + 2b deal with 'hosts' - I usually check VST on both of these but I'm not sure if this really matters.
3. 'OS' -- choose your operating system - mine's Windows.
4. "Include' -- in this case you'd probably want to check 'free' only just to see what's out there.
5. 'Sample formats' - I usually leave this on the default which is 'any/ignore'.
6. 'Receptor Compatability' -- not being a Receptor owner I leave this @ the default which is 'ignore'
7. 'Development Environment' - leave this at 'All/Ignore'.
8. 'Sort by' - leave this at 'Developer' for now while you're searching but later on you may want to change it to a specific plugin you're looking for.
9. 'Results per Page' - I usually leave this at the default which is 15.
Recommended: RGC Triangle II, e-phonic Drumatic, EVM Synths Bassline,
AudioNerdz Delay Lama (for laughs), Ugo's Motion, Rez, String Theory and Texture, SuperwaveP8,
ReFx Claw, Majeken's Chimera and SubDuer, Ichiro Toda's Synth1, HG Fortune's Proto Plasm and Fuzzpilz Oatmeal.
There are hundreds of free VSTi's and this list is by no means all of the worthwhile ones --- there's new ones being released daily and it would be a part time job just to keep up with them.
The next category you'd probably want to explore is VST effects and there are just as many if not more of those in the 'free' category -- notable for their good quality are those by Kjaerhus. The search procedure is basically the same as it is for free instruments, except with 'effects' checked.
Good luck!