Need most effective UI tech options to work with .net 3.5.

We have a web application built in .net 3.5, we need to change the ui and some business functionality. The requirement mainly include 1. Adding collapsible panel 2. Adding filters in each column header of grids- text box where user can type the filter value ( allowing partial search), in some columns text box + drop down allowing users to type in or select the option from drop down, also the drop down should have checkboxes to select multiple values at a time for filtering. 3. Performance optimisation Need suggestions what UI technology can be used to get all these features in existing.net application. Thanks.