>I did do some quick testing by using the PREVIEW button and then getting back out without sending the message. I'm not real familiar with tags, so I was hoping that there was a list somewhere of all the valid tags.

Almost all HTML works in the messages. The best suggestion is to just get in the habit of hitting the PREVIEW button. Not only will it test your HTML, but it will also save you from potentially embarassing typos. Not that this has ever happened to me. :)