Here’s a reference to something every site should have: a custom error page. If someone mistypes a URL on your domain, what do they see? That little bit of standard “page not found” text? They wanted to be on your site, so you should be giving them more than that. In An Absolute Pointless Custom 404-Error Page, the E-Marketing Performance blog shows how someone has gone to the effort of creating their own error page, then wasted that effort. Don’t do the same.
If your site doesn’t have a custom error page (type in some garbage after your domain name to see) then it’s time to get one set up.