J2J provides an intuitive way to convert Java to JSON and JSON to Java. Annotate any Java class then use JsonWriter to emit JSON from java or JsonReader to convert JSON to java objects. (sourcecode and tutorial included) Version 2.0 in development.
DynAjax is a Javascript / ASP.Net / C# Framework easing dynamic calls to business / service C# methods directly from JavaScript code (like DWR framework does in Java World). The object serialization is based on JSON, permitting complex objects exchange.