ASP.NET MVC DropDownListFor with model of type List

To make a dropdown list you need two properties:

1. a property to which you will bind to (usually a scalar property of type integer or string)
2. a list of items containing two properties (one for the values and one for the text)

In your case you only have a list of string which cannot be exploited to create a usable drop down list.

While for number 2. you could have the value and the text be the same you need a property to bind to. You could use a weakly typed version of the helper:

@model List<string>
@Html.DropDownList(
    "Foo", 
    new SelectList(
        Model.Select(x => new { Value = x, Text = x }),
        "Value",
        "Text"
    )
)

where Foo will be the name of the ddl and used by the default model binder. So the generated markup might look something like this:

<select name="Foo" id="Foo">
    <option value="item 1">item 1</option>
    <option value="item 2">item 2</option>
    <option value="item 3">item 3</option>
    ...
</select>

This being said a far better view model for a drop down list is the following:

public class MyListModel
{
    public string SelectedItemId { get; set; }
    public IEnumerable<SelectListItem> Items { get; set; }
}

and then:

@model MyListModel
@Html.DropDownListFor(
    x => x.SelectedItemId,
    new SelectList(Model.Items, "Value", "Text")
)

and if you wanted to preselect some option in this list all you need to do is to set the SelectedItemId property of this view model to the corresponding Value of some element in the Items collection.