RSS Validator from Mark Pilgrim & Sam Ruby is up and running, I think Mark had a couple of very intensive days correcting not-obvious problems (like commas in URLs) after they went live. Today only Vote for your favorite "Valid RSS" banner!

Ps. Not sure where the logo went, but a bit additional info : the code's open source, written in Python & will run locally - see
about. Also - SOAP is on the way (woo-hoo!!).