Browsing on the KVR database (the best place for VSTi)
I found String Studio:
http://www.applied-acoustics.com/
which is amazingly modelling lots of stringed and non-stringed
instruments.
On their website you can download demos of Tassman (known
from the early VST soft-synth days) and other fantastic stuff.
Their software is not a huge, 100 GB collection of samples.
They use modelling algorythms, therefore only a few MB to
install/run.
Cheers
Djordje
www.midiguitar.de