Custom Tooltip and Popup

Like with everything else in WPF you can override the style for tooltips.

Standard Tooltip

Custom Tooltip

<Window.Resources>
    <Style x:Key="CustomTooltip" TargetType="{x:Type ToolTip}">
        <Setter Property="HorizontalOffset" Value="50" />
        <Setter Property="VerticalOffset" Value="-50" />
        <Setter Property="Background" Value="Beige" />
        <Setter Property="Foreground" Value="Gray" />
        <Setter Property="FontSize" Value="18" />
        <Setter Property="FontFamily" Value="Segoe UI" />
    </Style>
</Window.Resources>

<!-- the following code lives inside the control you want to tooltip -->
<Grid.ToolTip>
    <ToolTip Style="{StaticResource CustomTooltip}">
        <TextBlock>Custom tooltip</TextBlock>
    </ToolTip>
</Grid.ToolTip>

This custom tooltip rather boringly just features a textblock but you can customise with any fonts and colours and include any combination of UI controls such as images, animations or even video.

Source:  http://stevenhollidge.com/blog-source-code/WrappingListbox-CustomTooltip.zip

Custom Tooltip with Shape (Path)

<Style x:Key="{x:Type ToolTip}" TargetType="ToolTip">
    <Setter Property="OverridesDefaultStyle" Value="true" />
    <Setter Property="HorizontalOffset" Value="0" />
    <Setter Property="VerticalOffset" Value="-75" />
    <Setter Property="Background" Value="GhostWhite" />
    <Setter Property="Foreground" Value="Gray" />
    <Setter Property="FontSize" Value="12" />
    <Setter Property="FontFamily" Value="Segoe UI" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ToolTip">
                <Canvas Width="200" Height="100">
                    <Path x:Name="Container"
                          Canvas.Left="0"
                          Canvas.Top="0"
                          Margin="20"
                          Data="M 0,40 L15,50 15,80 150,80 150,0 15,0 15,30"
                          Fill="{TemplateBinding Background}"
                          Stroke="Black">
                        <Path.Effect>
                            <DropShadowEffect BlurRadius="10"
                                              Opacity="0.5"
                                              ShadowDepth="4" />
                        </Path.Effect>
                    </Path>
                    <TextBlock Canvas.Left="50"
                               Canvas.Top="28"
                               Width="100"
                               Height="65"
                               Text="{TemplateBinding Content}"
                               TextWrapping="Wrapwithoverflow" />
                </Canvas>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Source:  http://stevenhollidge.com/blog-source-code/WrappingListbox-CustomTooltip-WithPath.zip

Popup

<Popup x:Name="PopupInfo"
       AllowsTransparency="True"
       HorizontalOffset="-10"
       IsOpen="{Binding ElementName=backgroundGrid,
                        Path=IsMouseOver,
                        Mode=OneWay,
                        UpdateSourceTrigger=PropertyChanged}"
       VerticalOffset="-30"
       Placement="Right">

    <Canvas Width="200" Height="100">
        <Path x:Name="Container"
              Canvas.Left="0"
              Canvas.Top="0"
              Margin="20"
              Data="M 0,40 L15,50 15,80 150,80 150,0 15,0 15,30"
              Fill="Beige"
              Stroke="Black">
            <Path.Effect>
                <DropShadowEffect BlurRadius="10"
                                  Opacity="0.5"
                                  ShadowDepth="4" />
            </Path.Effect>
        </Path>
        <TextBlock Canvas.Left="50"
                   Canvas.Top="28"
                   Width="100"
                   Height="65"
                   Text="Popup with text...."
                   TextWrapping="Wrapwithoverflow" />

    </Canvas>
</Popup>

Source: http://stevenhollidge.com/blog-source-code/wpf-popup.zip