Ive become a fan of using horzontal rules for this. Since what your doing is just applying a sort of meaningless element to just clear floats, using a div is sort of overkill. At least thats how I see it.
anyways either will work but with a little less CSS and HTML you can use:
or the XHTML
<hr class="clear" />
and the css of
IE6 (dont about 7) does give it a little spacing either the float or the hr itsself but it's some 6 pixels or so.