Actually, with MarsEdit you do get that. That's what MarsEdit's editor window is always showing you.
Unless you mean on the protocol level, in which case it's a bunch of XML, which you can see by showing the "RPC Console" and watching it while you send to your weblog.
But the content of your post is shown to you in the editor window, and it's usually HTML but can be other formats depending on how your weblog server is configured.