I am trying to add a hyperlink to my email signature but there doesn't seem to be anything that allows me to do this. Anyone know how?
Just figured it out! Open Word doc (I don't have iWork, but it may work with the doc program there, too), write the body text of your e-mail message and include urls. Go to File>Send To>Mail Recipient (as HTML). You can't edit the body after that, but you can add a subject line and addresses in the To: line.
Yes, it's a bummer that Entourage doesn't just do it, but this is an easy alternative.