Replaced with: The URL in the blog's Settings. Usage: A good value for a "home" link, or the "back to current" link in an archive template, e.g.
<a href="<$BlogURL$>">home</a>
Replaced with: The Title in the blog's Settings. Usage: The title in the page, e.g.
<h1><$BlogTitle$></h1>
<title><$BlogTitle$></title>
Replaced with: The Description in the blog's Settings. Usage: A subhead in the header, or at the top of a sidebar, e.g.
<h2><$BlogDescription$></h2>
Replaced with: The Archive Filename in the blog's Settings. Usage: Either a link to the archive index page (for blogs with a separate index page), e.g.
<a href="<$BlogArchiveFileName$>">archives</a>
<script type="text/javascript" src="<$BlogArchiveFileName$>"></script>
Although the "Template Help" at the bottom of the main template editing page has listed it for more than a year now, <$BlogItemURL$>, which apparently had something to do with the first version of Blogger Pro, doesn't have any meaning, and isn't replaced by anything.