Even if you aren't using XSLT on your sites, you've probably considered using RSS feeds to keep your visitors informed. The ability to quickly preview RSS and convert to HTML is one of the options you get with this XSL transformations plugin.
TMXSLT plugin makes it easier to insert XSLT (Extensible Stylesheet Language Transformations) code while acting as a quick reference. Includes XPath extensions. See also: TMCSS plugin.