createrawtransaction online
That's correct, a private key is not required to use createrawtransaction. The private key is only required during the signing process of signrawtransaction just as you stated in your question.  

If you are looking for a web service that will allow you to create a raw transaction online, I suggest you check out http://coinb.in it does exactly this, as well as broadcast the transaction, and allow you to save a local copy to sign the transaction offline.