CompositeCollection

<ListBox Name="myListBox" Height="300" Width="200" Background="White">
      <ListBox.ItemsSource>
        <CompositeCollection>
          <CollectionContainer
            Collection="{Binding Source={StaticResource GreekGodsData}}" />
          <CollectionContainer
            Collection="{Binding Source={StaticResource GreekHeroesData}}" />
          <ListBoxItem Foreground="Red">Other Listbox Item 1</ListBoxItem>
          <ListBoxItem Foreground="Red">Other Listbox Item 2</ListBoxItem>
        </CompositeCollection>
      </ListBox.ItemsSource>
    </ListBox>