Spitfire Audio is a plugin maker that has sampled the BBC Symphony Orchestra. If you answer a questionnaire on their web site and wait two weeks (no, I have no idea what that’s about) you get the slimmed down but still great Discover version of the plugin. It has 33 instruments arranged into groups (two violin sections, one with violas, basses, cellos, percussion, bells, harps etc.). Each instrument group has multiple techniques, like long, spiccato, pizzicato and tremolo for violins.
The fullest version of the plugin, Professional, has 57 instruments with round-robin samples for each instrument, customizable techniques, mic positions and legato. . Discovery has 33 instrument with a single sample for each note of each instrument, and fixed techniques etc. But it’s still great for say a symphonic intro.
Here’s a test I made making one such symphonic intro for a metal song:
Tip: how you use the plugin is a bit non-intuitive. You need one instance of the plugin for each instrument / technique combo. So violins 1 long is one track, violins 1 pizzicato is another, cellos long a third etc. So a complete symphonic arrangement will be a lot of tracks.
If you want to learn how to make a full orchestral arrangement, here’s a great tutorial: