<abbr> = abbreviation

<acronym>

<address> (often slightly indented and italic)

<cite> = short citation (typically italic)

<code> = code fragment (typically monospaced)

<dfn> = definition (terms used for first time, typically italic)

<em> = emphasis (typically italic)

<kbd> = keyboard input, i.e., text that should be entered by the user (typically monospaced)

<q> = short quotation

<samp> = sample of text which should be used literally (i.e., text qua text)

<strong> (typically boldface)

<tt> = teletype (monospaced)

<var> = variable

 

<del> = deleted text

<ins> = inserted text

You are my <del cite="http://www.crap.com/useless.htm" datetime="2004-06-05T10:36:47-07:00">worst enemy</del><ins cite="http://www.kisses.com/treats.htm" datetime="2004-06-05T10:36:56-07:00"> best friend</ins>.

You are my worst enemy best friend.

---

You are my <del cite="http://www.crap.com/useless.htm" datetime="2004-06-05T10:36:47-07:00"><!-- worst enemy --> </del><ins cite="http://www.kisses.com/treats.htm" datetime="2004-06-05T10:36:56-07:00"> best friend</ins>.

You are my best friend.

 

<pre> means

preformatted – with line breaks and spaces and all, as set in the code. 
    Or, for that matter, lack of line breaks – look out for that, as the text can run right off the right edge.
    It's typically rendered in a monospaced font.
    It's a <p>-level tag, and you can use most HTML markup inside it, 
such as italics.