Here’s a small handful of characters I find myself using a lot.  It makes for a cleaner HTML if you use the code vs. pasting in some version of it from another document (like MS Word) which may actually be  using a non-standard character and not appear correctly on everyone’s computer.  So, when possible, I use the following HTML codes:

&	&
“	"
<	&lt;
>	&gt;
»	&raquo;
«	&laquo;

Registered TM ®	®
Copyright ©	©
Non-Breaking Space	 

You can find other information character codes here:
http://www.htmlhelp.com/reference/charset/

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Cheers,
Kelly
Beaverton Web Design