Link button in wpf

If you don't want any of the normal Button style and just want something that looks like a hyperlink you could start with this

<Button Margin="5" Content="Test" Cursor="Hand">
    <Button.Template>
        <ControlTemplate TargetType="Button">
            <TextBlock TextDecorations="Underline">
                <ContentPresenter />
            </TextBlock>
        </ControlTemplate>
    </Button.Template>
    <Button.Style>
        <Style TargetType="Button">
            <Setter Property="Foreground" Value="Blue" />
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="true">
                    <Setter Property="Foreground" Value="Red" />
                </Trigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Here's the same as a style:

<Style
    x:Key="LinkButton"
    TargetType="Button">
    <Setter
        Property="Template">
        <Setter.Value>
            <ControlTemplate
                TargetType="Button">
                <TextBlock
                    TextDecorations="Underline">
                <ContentPresenter /></TextBlock>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
    <Setter
        Property="Foreground"
        Value="Blue" />
    <Style.Triggers>
        <Trigger
            Property="IsMouseOver"
            Value="true">
            <Setter
                Property="Foreground"
                Value="Red" />
        </Trigger>
    </Style.Triggers>
</Style>

and you can use it like this:

<Button Style="{StaticResource LinkButton}" Content="Clicky" />

The easiest way (I do this in my application):

<TextBlock Name="..."
   Text="..."
   Cursor="Hand"
   Foreground="Blue"
   TextDecorations="Underline"
   MouseLeftButtonUp=..."
/>

you have full control on TextDecoration, e.g. change pen style or offset. take a look at this link to find out more: http://msdn.microsoft.com/en-us/library/system.windows.textdecorations.underline.aspx

Why do you not want to use Hyperlink?

<Button>
    <Hyperlink>
</Button>

Combination of all proposed solutions:
Completed style, as in the accepted version, but without hardcoded values.

<Style
    x:Key="HyperlinkButton"
    TargetType="{x:Type Button}"
    BasedOn="{StaticResource {x:Type Button}}"
    >
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <TextBlock>
                    <Hyperlink
                        Command="{TemplateBinding Command}"
                        CommandTarget="{TemplateBinding CommandTarget}"
                        CommandParameter="{TemplateBinding CommandParameter}"
                        >
                        <ContentPresenter />
                    </Hyperlink>
                </TextBlock>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>