This is a list of sites on the World Wide Web that you can use to check your html code. I have prepared a brief description of each site, so you can get an idea of which to use.
Different sites check the code against different levels of the HTML standard.
Bobby Bobby is a HTML checker designed by the Center for Applied Special Technology. Weblint This is a more general HTML checker. It's output is friendlier than the HTML validator and also checks for some of the more common mistakes. Weblint now charges for its services at this site. However you can submit documents of less than 2k for free.