Hi,
If you provide the Date part before binding, I mean in your Query, then binding code is very simple:
<asp:dropdownlist datasource="DataSourceName" datavaluefield="id" datatextfield="d" ... />
<asp:sqldatasource
id="DataSourceName"
runat="server"
ConnectionString="<%$ ConnectionStrings:ConNameInConfig%>"
SelectCommand="SELECT id,year(date) as d FROM tblName"
</asp:sqldatasource>
I hope it helps.