Hi Dan,
You can use RadChart custom GridLine functionality which allows you to display grid lines (both horizontal and vertical) on any value you want. Here is a small example:
You can find more information on custom GridLines in our online help system
here.
If you have any other questions about RadChart for WPF please ask them in the proper category. This way other people that have similar problems can help you too.
All the best,
Yavor
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.