You should only talk to your own nodes through RPC. In the conf file you need to specify a user and password and IP range for RPC to talk to.

If you need to pull other information there are various services that allow for API calls, but since access to RPC more or less means you have access to the wallet that is there you are probably not going to be able to find anyplace that allows remote calls. It's just basic bitcoin security and security in general.

-Dave