I believe that best way is to set clear:both to the upcoming element.
Here's why:
1) :after selector is not supported in IE6/7 and buggy in FF3, however,
if you care only about IE8+ and FF3.5+ clearing with :after is probably best for you...
2) overflow is supposed to do something else so this hack isn't reliable enough.
Note to author: there is nothing hacky on clearing... Clearing means to skip the floating fields. CLEAR is with us since HTML3 (who knows, maybe even longer) http://www.w3.org/MarkUp/html3/deflists.html , maybe they should chose a bit different name like page: new, but thats just a detail...
