Here's my first shot at a public jQuery plugin. It uses jquery.date_input.js as well. My goal was to replicate the Google Calendar start date/end date picker. Check out the GitHub page for full features! Their system implements some "smarts" when it comes to modifying the end date based on the start date, which is what I liked.
in reference to: nickspacek's jQuery-DateSpanPicker at master - GitHub (view on Google Sidewiki)