Is there any control which is equivalent to Windows Forms ComboBox in ASP.Net

There is no ComboBox in ASP.Net, there is DropDownList. Still if you need to use ComboBox you can make use of AJAX Control Toolkit ComboBox

You need to download the AjaxControlToolkit Dll.

Create a folder under your root directory with name as Bin

Paste the Dll in the folder.

After that you have to register it like this on the page where you want to use Ajax Controls

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

Thank You.

Yes you have to get it separately, you need to download the DLL and add reference and then use its controls