public IEnumerable<LibraryViewModel> Libraries {
    get {
        if (!string.IsNullOrEmpty(this.LibrarySearchString))
            return _libraries.Where(lib => IsLibraryMatch(lib, this.LibrarySearchString));
        else
            return _libraries.OrderBy(lib => !lib.IsFavourite);
    }
}

<con:FilterListBox Grid.Row="1"
                   ItemsSource="{Binding Libraries}"
                   SelectedItem="{Binding SelectedLibrary}"
                   ItemTemplate="{StaticResource
                                  LibraryItemTemplate}"
                   SearchString="{Binding LibrarySearchString, Mode=TwoWay}"
                   IsSearching="False"
                   Margin="4"/>

<Style x:Key="{x:Type con:FilterListBox}" TargetType="{x:Type con:FilterListBox}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type con:FilterListBox}">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto"/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>

                    <DockPanel Grid.Row="0">
                        <TextBlock Text="Search"
                                    VerticalAlignment="Center"/>
                        <TextBox Text="{Binding RelativeSource={RelativeSource TemplatedParent},
                                                Path=SearchString,
                                                UpdateSourceTrigger=PropertyChanged}"
                                 Margin="4,0,0,0"/>
                    </DockPanel>

                    <ScrollViewer Grid.Row="1" CanContentScroll="True">
                        <StackPanel IsItemsHost="True"
                                    HorizontalAlignment="Stretch"/>
                    </ScrollViewer>

                    <TextBlock Grid.Row="1"
                               Text="Searching..."
                               HorizontalAlignment="Center"
                               VerticalAlignment="Center"
                               Visibility="{Binding RelativeSource={RelativeSource TemplatedParent},
                                                    Path=IsSearching,
                                                    Converter={StaticResource CollapsedIfFalseConverter}}"/>
                </Grid>

            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>