- Use the jQuery Multiple File Upload Plugin. An example showing how to use it with ASP.NET with code in VB.NET
- Use a Flash based component to upload multiple files in a medium-trust hosting environment. This has a Progress Bar too.
Also see:
HOW TO implement AutoComplete with jQuery & ASP.NET
Generate Dynamic Tooltips with ASP.NET & jQuery
ASP.NET File Uploads: Threats & Counter-Measures