When developing a theme for WordPress, we talked about the importance of a good theme header, the header.php file. This includes not just the mast head of the HTML document that you see, but also the head tag, which includes the doctype, title, CSS links, and more.
Likewise, it is important to close with a strong footer. This will include both the visible footer to your website, assuming that it has one, but also close any tags you opened in your header. These would include any containers, as well the body and html tags.
Additionally, you will probably want to have a a div to clear out any remaining floats, or define that for your footer class/id in your CSS document.
As before, it is good to have strong comments so you can tell that closing tag goes with what section. Likewise, you will probably want to include PHP comments in the PHP sections of the file.
A typical footer.php would look something like the following: