For the most detailed and complete orchestral instruments, take a look at the Vienna Symphonic Library: http://www.vsl.co.at/
They have a huge range, from single download instruments through their Special Edition to the large DVD collections. The instruments play in VSL's own plugin called Vienna Instruments (free) or in the more detailed Vienna Instruments Pro.
There are lots of audio examples and details at their website. I have many of their products and they are exceptional.