Some of the links to the tools at the start of this thread are great, but the w3 validation tool seems totally pointless to me.
My site came up with 69 errors, so I checked Google.com and it had a similar amount and this site has it's fair share-
http://validator.w3.org/check?uri=ht...ebproworld.com
Personally I think that the W3 validator is a complete waste of time, if your website works ok in most browsers than who cares if W3 find petty little faults with it?
The sitereport card is a very useful tool and is saved to favorites.