Let me announce libnmcrpc:
https://gitorious.org/libnmcrpc This is a C++ library that implements a JSON-RPC client to talk to the RPC interface of Namecoin or Bitcoin. While I wrote it for Namecoin and will be using it that way, the general RPC calling mechanism (which is the part already implemented) can talk to Bitcoin (and other coins I presume) just as well. I'm planning to add higher-level functions for Namecoin features in the future, but this will not impact its ability to be used also with Bitcoin if the correct RPC calls are formulated manually.
I'm posting this here in case someone finds it useful, it is free software (LAGPLv3). Note that it is still very much work in progress, but in my tests the RPC calls worked already fine.
