Also, don't forget Project Sam; they do excellent Brass and Percussion libraries,with 3 mic positions.
However, recently, for utterly convincing Ochestral Brass, I've been using something that isn't based on samples.
It's called Wallander Brass Instruments and uses a form of additive synthesis. Though this may sound hokey, it sounds for the most part, absolutely amazing and has an expressiveness that is beyond anything else out there.
You really 'play' the instrument as opposed to triggering different samples with keyswitches.
You use a midi controller for breath, so the louder you blow, the more volume and more fortissimo you play. Staccato notes are played by playing shorter notes, portato slightly longer, and you can use aftertouch for vibrato.
So, you can actually play melodies the way you hear them in your head, as opposed to having to setup keyswitches etc. first.
The collection has 4 horns, 3 trumpets, 3 trombones and 2 tubas (no basstrombone unfortunately). These are all seperate instruments, which means you can play proper divisi (i.e 4 horns in unison, or a 4 part chord played by 4 seperate horns)
It has shades of physical modelling, but to my ears sounds more realistic while still retaining a similar level of control.
Although they can sound somewhat harsh and forward straight out of the box, with careful eq and a splash of Altiverb, as well as a bit of setting up, I've managed to create a convincing 'Hollywoo' like sound.
Wallander Instruments
For strings, I've always liked the tone of Sonic Implants (now Sonivox).
Cheers,
Joris