The "JSON in Java" ported to Unity C#. It is the same library used by Android Java, allowing copy/paste between native code and script. Easy to use, only two files, and properly handles nested quotes.
Example:
JSONObject jo1 = new JSONObject();
jo1.put("count", 1);
jo1.increment("count");
JSONObject jo2 = new JSONObject("{\"quote\": \"He said, \\\"I like JSON\\\"\"}");
JSONArray ja1 = new JSONArray();
ja1.put(jo1);
ja1.put(jo2);
See readme.txt for additional example code and references.