For checking website standards best site is validator.w3.org also can refer w3.org.Also can perform Acid3 Browser TestAcid3 is the third in a series of test pages written to help browser vendors ensure proper support for web standards in their products.
the best one is w3c standards first u can install this w3c than u check ur site is proper standards or not.
http://validator.w3.org <== This is website you need ! -- I'm Michael. Reviewer of http://citywpthemes.com