I compose alot of orchestral music and I prefer using Garritan Personal Orchestra and Edirol Orchestral, but of course both of them are commercial (and of course, I haven't got concious enough to use them illegaly *whistle*)
For a summary of VST plugins you can use MadTracker.org's database over common, and often free, VST. Both effects and instruments. That you can find here.
And last there's an excellent site for VST-junkies here.