MVC3 DropDownListFor - a simple example?

I'm having trouble with DropDownListFor in my MVC3 app. I was able to use StackOverflow to figure out how to get them to appear on the View, but now I don't know how to capture the values in its corresponding properties on the View Model when it's submitted. In order to get this to work I had to create an inner class that had an ID and a value property, then I had to use an IEnumerable<Contrib> to satisfy the DropDownListFor parameter requirements. Now, however, how is MVC FW supposed to map the value that is selected on this drop-down back into the simple string property on my view model?

public class MyViewModelClass
{
    public class Contrib
    {
        public int ContribId { get; set; }
        public string Value { get; set; }
    }

    public IEnumerable<Contrib> ContribTypeOptions = 
        new List<Contrib>
        {
            new Contrib {ContribId = 0, Value = "Payroll Deduction"},
            new Contrib {ContribId = 1, Value = "Bill Me"}
        };

    [DisplayName("Contribution Type")]
    public string ContribType { get; set; }
}

In my View I place the dropdown on the page like this:

<div class="editor-label">
    @Html.LabelFor(m => m.ContribType)
</div>
<div class="editor-field">
    @Html.DropDownListFor(m => m.ContribTypeOptions.First().ContribId, 
             new SelectList(Model.ContribTypeOptions, "ContribId", "Value"))
</div>

When I submit the form the ContribType is (of course) null.

What is the correct way to do this?