The following code can be used to force your form to the top of the z-order. Use this functionality with care since it's bad practice to hog the topmost position which could obscure other important functionality.
private void Form1_Load(object sender, System.EventArgs e)
{
//get handle
this.Capture = true;
IntPtr hwnd = OpenNETCF.Win32.Win32Window.GetCapture();
this.Capture = false;
//set foreground
OpenNETCF.Win32.Win32Window.SetWindowPos(hwnd, Win32Window.SetWindowPosZOrder.HWND_TOPMOST, 0, 0, 0, 0, Win32Window.SetWindowPosFlags.SWP_NOMOVE | Win32Window.SetWindowPosFlags.SWP_NOSIZE | Win32Window.SetWindowPosFlags.SWP_SHOWWINDOW);
}
Note that this code cannot be placed in the form constructor, since the native form has yet to be created so a valid window handle won't be returned. Here the code is placed into the Form_Load method.
In .NETCF 2.0 you can set the TopMost property of your form which removes the need for any of this interop (Thanks Daniel Moth for correcting this).