well for free, theres DSK Brass.... i use this sometimes myself. i think the sounds are synthesized.... so they are not the most realistic brasses ever but its free and tbh they are usable depending on what sort of sound your after
there was also a free russian vst called TPS Brass Section Module, but its apparently been banned because it uses samples from retail sample CD's
i did hear great things about it but then i tried it and tbh i wasnt impressed at all, the sounds were limited and it was EXTREMELY cpu heavy.... i takes up alot of room too so i uninstalled it
for realistic brass you would probably be better off with a multisampled brass section..... cant help you too much here as im after one myself...... oh and expect to pay, dont think you'll find a freeware one
heres a few names worth checking out though.....
Ueberschall Liquid Brass
AMG Kick Ass Brass