When things start coming together and your site is taking form how does everyone check the overall health and perfection of a site? For example.. websitegrader.com has a tool to get your "score" which I know is a rough estimate but how does everyone ensure they are not missing little things like alt text for example if they do not use something like this? The only thing ive ever really done is use the Web Developers toolbar "Error Console".. Fill me in pleaseee, thanks

W3C Validator
Google Page Speed Score addon for Firefox

Run a spellchecker over all your text content
Check in all popular browsers
Check for dead/incorrect links
Check things like contact forms are working

I continually check every aspect of the website I’m currently working on over and over to double check if there’s currently any problem with the design. It only takes one bad link to sway visitors and customers away.