If you're on a budget the Session Horns are a good deal for the $. I used the trumpets in combination with real saxes on a my tune Funky Boulevard you can find link in my sig. 
 
I listened to the fabelsounds stuff and it really sounds nice but the Broadway lites is $500 
 
If you are looking for realistic solo instruments check out the Samplemodeling that was recommended. It sounds amazing and works well with a wind controller. I have been lusting after them for a while now to use with my wx5. So far I have resisted.

John
Why did the OP have to start this thread. Loptec's post has me going to my piggy bank and looking in it hearing nothing but an echo.

 

Yeah! The guys at Samplemodeling are amazing! :)
I just uploaded a little video of a cover song I'm currently working on where I'm using Samplemodeling's Trombone, Horns and Tuba.
First I've soloed out the brass and then I play the same bit again with all instruments included.
http://youtu.be/EfMw6Q1HoIY

Guitarhacker
The secret to emulating ANY instrument with sampled synths is in the articulations and the details.... basically, you need to be able to get inside the head of how a real player of that instrument would play it, then, be able to translate that to midi.

Lacking that, the best samples will sound fake.

On the other hand, using a halfway decent sample or midi patch, (TTS or GPO) put the details where they should be and you will have a very convincing track.

 
I couldn't agree more! 
To make an instrument sound real it's not enough with nice sounding sample libraries.
It's all in the performance..
I think the most important things have been mentioned here already.. But anyway..
Here's a list of a few basic things that I always keep in mind when trying to make "real acoustic sounding" MIDI-tracks:

1. If the (acoustic) instrument just have one voice (like a trumpet, for example); make sure to stay true to this!
   You may want a whole brass section, but never play chords like on a piano. In a brass section each voice is an individual musician with his/her own style of playing and this is something you want to mimic with MIDI. SO: Load one instrument for each voice/player you want. By doing this you have full control over bends, volume and expression for each player which brings life to each voice.
2. About quantizing: I agree one should never just quantize to closest 16th note or what ever. Not quantizing will absolutely make it feel less like a machine. BUT: Just choosing not to quantize won't necessarily make the performance more alive! A good musician doesn't "miss" the beat by accident, but shifts the timing to get the right feel. It's ALL about the right feel.
3. Note length: One thing that might be easy to forget is the length of the notes, even though this is just as important as the timing to make the performance feel real. If all notes are precise 16th notes, this also will make it feel more machine like. Turn off snap and fine tune the lengths of the notes.
4. Now when you're split up all voices into separate tracks, try to imagine each voice in the brass section as it's own melody. Of course it's important that each voice sound good with the rest in the brass section, but it's just as important that each voice sound good in it self. Make sure each voice has it's own flowing natural melody.

..I think I could go on like forever with this list.. But ..
..A good thing would be to listen a lot to real performances and focus on the instrument you want to mimic... And I mean listen to the individual instruments.. not just "the brass section". Everything lies in the details!

Edit: 2nd dual post tonight!

I've been very pleased with the horns in EastWest Symphony Orchestra. Lots of options to put together a really convincing track.
 
Regards,
Dan
 

I own BBB and couldn't live without them ever again... :)