TinyMce has an api for accessing content from the editor.
This code will grab the html from the active editor:
// Get the HTML contents of the currently active editor
tinyMCE.activeEditor.getContent();
// Get the raw contents of the currently active editor
tinyMCE.activeEditor.getContent({format : 'raw'});
// Get content of a specific editor:
tinyMCE.get('content id').getContent()