Is there any readymade free online tool available that checks whether the site is compatible to W3C standards?? eg, does it have proper use of tags and links etc..
... and then if you want to test your sites level of accessibility run it through this online accessibility checker based on Cynthia Says: http://www.contentquality.com/
If you use Mozilla Firefox there's 2 extension that's worth to install. Web Developer Toolbar and HTML validator.
The only truly official validators are at http://W3C.org, aka W3.org (e.g. http://validator.w3.org/). Yes I personally make sure my site http://EnvironmentalChemistry.com validates to HTML4.01 Strict and CSS specifications.
I also think theres a dreamweaver exchange plugin as well - that way you can keep an eye on your code as you code it.
Fellers, get the Tidy Firefox plug-in: http://users.skynet.be/mgueury/mozilla/ You can check your sites as you build them and see how well other sites are coded. An excellent tool.