Add a drop down list to your page / control. Then in your code behind something like
foreach (var manufacturer in ManufacturerManager.GetAllManufacturers()) { ddlManufacturers.Items.Add(new ListItem(manufacturer.Name, manufacturer.ManufacturerID.ToString())); }
in your selected index changed event of the drop down list grab the selected id (int.parse(ddlManufacturers.SelectedItem.Value)) and construct your redirect url.