Validate File types

http://www.aspsnippets.com/Articles/jQuery-Plugin-to-validate-File-Types-and-Extensions-in-ASP.Net-AsyncFileUpload-Control.aspx

Multiple File hosting using ASP.Net and jQuery

http://www.aspsnippets.com/Green/Articles/Multiple-File-Uploads-Gmail-Style-using-JQuery-and-ASP.Net.aspx