I've thought for a while now that browsers probably shouldn't allow POST requests for another domain (especially scripted ones). Unfortunately that would break lots and lots of web applications so the chances of it being implemented are somewhere around zero.

One thing that might help a bit is to set up your webserver to prohibit POSTs that don't have a referer header from your trusted site(s). I'm pretty sure there's a way to do that in apache.

As far as I know you a malicious site can't fake a referer header* (unless maybe if you allow cross-site XMLHTTP - but all modern browsers prohibit that - right?)

Good suggestion on the tokens, by the way.