Check out the JQuery UI Datepicker.
Your case is a bit special since the ID is generated dynamically but it is still pretty easy:
$("span[id^='date-']").datepicker();
Taking a closer look, I just realized that you are trying to tie the datepicker to a span where it would normally be assigned to a textbox. So really what you are going to want is to add a textbox and then do this:
$("input[id^='date-']").datepicker();
Also make sure that you have the jQuery UI CSS referenced. Something like this on your page or site.master:
@import url(/Content/ui.all.css);