I always assumed that "judgement" is the correct spelling, but when my Word 2003 spellchecker complained about it (with the language flavour set to US English) I looked it up in the Concise Oxford English Dictionary (I have an electronic version, of course) and found this interesting entry:
"In British English the normal spelling in general contexts is judgement. However, the spelling judgment is conventional in legal contexts, and in North American English".
