Silverlight - how do I get the text of the selected item in a combobox

The selected item of your combo box is whatever type of item is currently holding. So if you set the binding to a collection of strings, then the selected item will be a string:

string mySelectedValue = ((string)MyComboBox.SelectedItem);

If it is a more complex object you will need to cast and use the expected object. If you have XAML using the list box item class, like:

<ComboBox x:Name="MyComboBox">
    <ComboBox.Items>
        <ComboBoxItem>
            <TextBlock Text="Hello World"/>
        </ComboBoxItem>
    </ComboBox.Items>
</ComboBox>

Then you would access the selected item like this:

string mySelectedValue = 
  ((TextBlock)((ComboBoxItem)MyComboBox.SelectedItem).Content).Text;

Right, the answer is to use myCombo.SelectionBoxItem.ToString()

For a complex object, use reflection with the DisplayMemberPath property:

var itemType = cbx.SelectedItem.GetType();
var pi = itemType.GetProperty(cbx.DisplayMemberPath);
var stringValue = pi.GetValue(cbx.SelectedItem, null).ToString();