Considering you have a GUI Crosshair texture, here's the code you use.

var crosshairTexture : Texture2D;

var position : Rect;

function Start() { position = Rect( ( Screen.width - crosshairTexture.width ) / 2, ( Screen.height - crosshairTexture.height ) / 2, crosshairTexture.width, crosshairTexture.height ); }

function OnGUI() { GUI.DrawTexture(position, crosshairTexture);
}

...and that's how. about that 2d rotator thing... I absolutely have no idea. PS make sure to have the GUI Crosshair set into the script. remember, the script is in the camera!

Try this answer. It should solve the 2D Rotation issue.