HTML Tidy
Mike Sax: In order for XHTML in RSS to reach critical mass (and thus become a standard), we need to do the following...
I use HTML Tidy. It runs on all the major operating systems. It has a Java port and a Perl interface. Jon Udell has even documented how to use it with Radio and why.
Once usage of XHTML in RSS feeds is documented, I'll add explicit support to the RSS validator.