Most banner tools have some selection of fonts but ImageMagick has a way to use any font you can find one the web. This allows you to use specialy fonts like dings and holiday fonts.
Find a font: You can use any search engine to find free fonts or a search engine that specializes in fonts like free-fonts.com. One site that is webtv friendly is Absolute Fonts Archive. At some other sites the fonts come zipped so you have to know how to unzip them.
Getting the URL: So you find a cool font like LokiCola but when yu click the link you get the message WebTV can't use this.... Hit your GoTo key then Show Last. Save that URL in a clipboard.
Go to your clipboard, copy the URL of the font and back up till your back on the Annotate page. Paste it in the box under the selection of fonts built into ImageMagick
Select a color and size. 50 is a good size to try first. For Gravity, select center.