I think that Yellow Tools \"Pure Guitars\" offers some of the finest nylon string instruments available. This collection offers three versions - a spanish guitar, a classical and a classical with vibrato, suitable for solo note lines. (There are also some excellent steel string patches, but for me the nylons are the standouts.)
The nylon gtrs are beautifully recorded,expertly velocity-switched, expressive, evocative and have lots of extras such as string noise, fret noises, harmonics which are quite useful, but must be employed tastefully, though. Key-switching in the lower octaves brings in harmonics and fx.
I also own Hans Zimmer 1&2 and these both offer good nylons. These patches are much smaller than \"Pure\" so great if you use hardware samplers. (They sound great in my Korg Triton.)Vol 1 has nice patches but they have quite significant vibrato on many patches. Vol 2 has the \"Flamenco guitar\" which has several patches, which are almost as good as the \"Pure guitars\" to my ears.
I also have Quantum Leap Guitars which has a servicable multisampled nylon with fx and other cool elements, but the tone of the other two libraries is more pleasing to me.
Also check out Roland\'s Latin EXP card for the JV/XV series - some very cool latin-style guitar sounds. And also I like ACID loop library \"Total Spanish Guitar\" for loops.
One of my personal projects involves the use of both live and sampled nylon-string guitars. In an ensemble setting, the \"Pure Guitars\" collection really shines through. I have made some utterly convincing recordings using this technique.
I\'m one of the people who chimed in with Z6 last time this issue came up, and I\'m here to tell you, a good classical guitar library hasn\'t been done yet. If anybody out there thinks they\'d like to do one, I\'d love to add my two cents\' worth.
Meanwhile, the physical modelling guys are making great strides in this direction. I just ran across this URL a couple of weeks ago: