Unity Script Reference:

static function Disc(rotation: Quaternion, position: Vector3, axis: Vector3, size: float, cutoffPlane: bool, snap: float): Quaternion;

static Quaternion Disc(Quaternion rotation, Vector3 position, Vector3 axis, float size, bool cutoffPlane, float snap);

static def Disc(rotation as Quaternion, position as Vector3, axis as Vector3, size as float, cutoffPlane as bool, snap as float) as Quaternion

Parameters

rotation	The rotation of the disc.
position	The center of the disc.
axis	The axis to rotate around.
size	The size of the disc in world space See Also:HandleUtility.GetHandleSize.
cutoffPlane	If true, only the front-facing half of the circle is draw / draggable. This is useful when you have many overlapping rotation axes (like in the default rotate tool) to avoid clutter.
snap	The new value after the user has modified it. Note: Use HandleUtility.GetHandleSize where you might want to have constant screen-sized handles.

Description

Make a 3D disc that can be dragged with the mouse.

Disc Handle on the Scene View.

	// Create a handle to rotate an object over 45 degrees on X and Y axis
	
	@CustomEditor (DiscValueModifier)
	class DiscHandle extends Editor {
		function OnSceneGUI () {
	        target.rot = 
	        	Handles.Disc(target.rot,
	        			target.transform.position,
	        			Vector3(1,1,0),
	        			5,
	        			false,
	        			1);
	        							
	        if (GUI.changed)
	            EditorUtility.SetDirty (target);
	    }
	}

And the script attached to this Handle:

	// Usage: Place this script on the Game Object you want to modify
	// the handle's rot with the disc
	
	@script ExecuteInEditMode()
	
	var rot : Quaternion = Quaternion.identity;
	
	function Update() {
		transform.rotation = rot;
	}