While the default DataForm in Silverlight 3 looks pretty good. You can add some flare to it by changing the background from solid color to a gradient of blue. You do so by adding the Background tag to your XAML for your DataForm.
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FFE8F3FC" Offset="0"/>
<GradientStop Color="#FF9BCCEE" Offset="0.108"/>
Here is an example of what it would look like.
I snagged it from this very nice tutorial on DataForms.