You should also take a look at the HTML character name and ASCII tables.

Many of these codes have readable short forms, such as, &amp; for &, &lt; for < and &gt; for >. These three codes are particularly common as the plain text forms would normally be interpreted as HTML tokens. Another useful code is &nbsp; for a non-breaking space -- this is not treated as white space and is thus useful for filling empty table cells. See: HTML character names for the list.