Not sure if you would consider investing in a plugin, but this is the one we use to send out HTML emails. There isn't a way that I know of, would be interested to see other responses.
We actually use an older version which works great, the new version is likely a lot improved.
With plug-in. There are several that send HTML email.
With web published FM. You can use PHP, for example, to send HTML in email.
-- sent from my iPhone4 --
Thanks to both of you I'l check out those plug - ins as ASAP