Ya, I'm really bored these days. Today, I wrote a generic XML Schema validator. Eventually, I want to expand this to validate common forms of XML like Google's sitemap. But, I noticed that each version of sitemap XML has it's own namespace. What a nightmare!
http://reblinks.therssweblog.com/xsd.validator.aspx
Update: I've also completed a Sitemap Validator, which re-uses the code from my XSD Validator.