[madars]

You can also make any existing page editable (and then back to non-editable):

   javascript:if(document.body.contentEditable=="true"){ document.body.contentEditable="false"; document.designMode="off"; document.body.spellcheck=true;} else { document.body.spellcheck=false; document.body.contentEditable="true"; document.designMode="on";}; void(0);

[chrismorgan]

If you’re putting the document into design mode (the best way of doing it), why are you also setting contenteditable on the body?

Shortened version of your bookmarklet, for fun:

  javascript:document.designMode=(document.body.spellcheck=document.designMode=='on')?'off':'on'