Google Analytics

Wow, I've got to hand it to Google – again – for offering an extraordinary application at no charge.  Google Analytics was formerly "Urchin", and cost about $500 monthly.  It's an extremely robust log analysis tool that allows detailed "drill down" examination of things like referrer logs, page views, and much more.  A very clever user friendly tool called "site overlay" allows you to explore the click through rates of a home page's (any page's?) internal links.   Very helpful in designing navigation for the site.