The Clear tag
Lately, it seems more and more people are using multiple consecutive <br> tags to format their userpage, or are making userboxes and leaving them with no special formatting afterwards. The former has the problem of not adapting to later changes to the page; the latter has the more serious problem of disrupting the flow of text and moving section headers around. Fortunately, a simple solution to both exists: Template:Clear. Usage notes have been added to that page.