SurveyMonkey has the ability to basically provide a callback site.
Another option using jquery to check the iframe for contents that indicated a completed survey. This will not work by directly linking to the survey through the iframe because you would then being attempting to access data across different domains.
$().ready(function(){
if($('#surveyFrameId').contents().find("div .embed_title").val() == 'Thank you for taking the survey!'){
// do something
}
setTimeout(arguments.callee, 10000);})
You could something as indicated in the post below to get around the cross-domain issues.