Bootsy's plugins are cool. All of the free Melda things are great, even better with the new upgrade. Voxengo has some really good stuff. SIR is a freeware convolution plug that works well. ShortCircuit is a decent freeware sampler. There are more.
Kjerhaus Classic Series has some good freebies (if you can still find them). The JS/Cockos stuff is ugly as hell but very capable. Definitely Variety of Sound, as mentioned above. Blue Cat Audio has some good freebies.
It's not pretty, but it sounds pretty damned good! Better than several pianos I have in paid-for collections.
Oh, and AmpliTube 3 Free! I have AmpliTube 3 and use it all the time, but the free version features the same sound quality, which is awesome, only with far fewer options. But they're still very usable and versatile.
There was an old Dr. Katz episode where he had a comedian on (I think it was David Cross) that did a bit about those people that justify buying something because "it was only a dollar."
Why'd you buy that lamp?
It was a dollar.
But it's broken in half and it doesn't even have a cord.
The Fish Fillets. Blockfish is a good compressor and the Spitfish is an excellent de-esser. I have had problems with Variety of Sound crashing in Cubase 7 (64 bit). I haven't tried J-Bridger yet so maybe that will fix it.