Are you looking for soft-synth stuff (VSTi's) to use with a DAW or hardware based?
I've been happy with my Roland XV-3080 and the SR-JV80 orchestral expansion cards. Software wise, you might look into Garritan Personal Orchestra (GPO). Very decent samples of most all orchestral instruments (violins, violas, cellos, etc.)
Can probably help better if we know spefically what you're looking for - hardware vs. software.