We (Rockpool) created an entire 'online consultation' system, where you input your requirements and are presented with a list of suppliers that match your specification, ordered by cost. Users are also able to complete a checkout process that allows them to purchase packages online.
The rich user experience specified by the client required me to use JavaScript creatively, and gave me a chance to push my skills in this area, as well as many others.
N.B. The current site has changed significantly since my involvement and does not reflect my work; however, I have kept the URL here for completeness.