I'm looking for a good server/client protocol supported in Python for making data requests/file transfers between one server and many clients.  Security is also an issue - so secure login would be a plus.  I've been looking into XML-RPC, but it looks to be a pretty old (and possibly unused these days?) protocol.
There is no need to use HTTP (indeed, HTTP is not good for RPC in general in some respects), and no need to use a standards-based protocol if you're talking about a python client talking to a python server.
Use a Python-specific RPC library such as Pyro, or what Twisted provides (Twisted.spread).
Best Python supported server/client protocol?