How to select object with mouse?

This is what I use for:

1. Display name on MouseOver.

2. Display selection if unit is clicked.

When you hover the mouse over an object, it displays the name of the unit, defined by the variable on it, when you move the mouse out, it fades the title out. You can also add display ALL names by holding down a key, in my case [ALT] but I commented out that part, since you have to add the [ALT] key in input manager for that part to work. When you click an object it will highlight/rotate it. If you click on another object, it will deselect the previous, oh and the rotating is on xy-plane, depending your setup you might have to change that. This script has to be attached to any object that has to have a name or hovering, or you can reverse engeneer the code for your likings. You can see the final result at this youtube video: http://goo.gl/jdtlG and the material I used on my selection plane (Honestly, I used a cylinder though, slimmed and fit in size, and the material I used for it was this: http://i47.tinypic.com/t6f9r6.jpg

For this to work:

1. You must have a collider on the object.

2. You must add a 3D text object as child called ObjectTitle.

3. You must add a plane (or cylinder) as child called ObjectSelection

The code:

             var Highlight_00 : Material;
 
             var Title_Name                 : String = "?";
     private var Title_ColorInitial         : Color = Color(1.0, 1.0, 1.0, 1.0);
     private var Title_ColorFaded         : Color = Color(0.0, 0.0, 0.0, 0.0);
     private var Title_EnabledByMouse     : boolean = false;
     private var Title_EnabledByKey         : boolean = false;
 
     private var myTransform_Main         : Transform;
     private var myTransform_Title         : Transform;
     private var myTransform_Selection    : Transform;
 
     
     function Awake ()
     {
         myTransform_Main                                 = transform;
         myTransform_Title                                 = myTransform_Main.transform.Find("ObjectTitle");
         myTransform_Selection                             = myTransform_Main.transform.Find("ObjectSelection");
         
         myTransform_Title.renderer.material.color         = Title_ColorFaded;
         
         myTransform_Selection.renderer.enabled             = false;
         myTransform_Selection.renderer.material         = Highlight_00;
     }
     
     function Update ()
     {
         if(Input.GetMouseButtonDown(0))
         {
             myTransform_Selection.renderer.enabled = false;
         }
         
         /* TO ENABLE THIS, ASSIGN ALT KEY BY NAME "ShowNamesTest"
         if (Input.GetButtonDown ("ShowNamesTest"))
         {
             Title_EnabledByKey = true;
             Custom_TitleEnable();
         }
         
         if (Input.GetButtonUp ("ShowNamesTest"))
         {
             Title_EnabledByKey = false;
             Custom_TitleDisable();
         }
         */
         
         if(myTransform_Selection.renderer.enabled == true)
         {
             myTransform_Selection.transform.Rotate(Vector3(0,1,0), Time.deltaTime*15);
         }
     }
     
     function OnMouseEnter ()
     {
         Title_EnabledByMouse = true;
 
         Custom_TitleEnable();
     }
     
     function OnMouseExit ()
     {
         Title_EnabledByMouse = false;
         
         if(Title_EnabledByKey == true)
         {    
             return;
         }
         
         Custom_TitleDisable();
     }
     
     function Custom_TitleDisable ()
     {
         for (var a = 0.0; a < 0.5; a += Time.deltaTime)
         {
             if(Title_EnabledByMouse == true || Title_EnabledByKey == true)
             {
                 return;
             }
             else
             {
                 myTransform_Title.renderer.material.color = Color.Lerp (Title_ColorInitial, Title_ColorFaded, a/0.5);
                 yield;
             }
         }
     }
     
     function Custom_TitleEnable ()
     {
         myTransform_Title.renderer.material.color = Title_ColorInitial;
     }
     
     function OnMouseDown()
     {
         yield;
         myTransform_Selection.renderer.enabled = true;
     
     }

Final words:

If you can't get this to work, or don't understand reverse engeneering the code, just ask and I will be more than happy to help you through it. This is the approach I used, not wanting to deal with raycast at all, and sorry if my coding formatting is weird, we all get stupid layout habbits over time.

For moving objects, there are two different approaches. The first is to make each piece responsible for moving itself. This approach uses OnMouseDown() OnMouseDrag() and OnMouseUp() in a script that is attached to each game piece.

The second approach is to use Raycasting (Physics.Raycast) to find objects and them a script outside of the game pieces moves them around. If you search this list for the "OnMouseDown" and "Raycasting" you will find numerous examples of each. As a starting point see:

Highlighting and Moving an Object

The script in @KraljCro question works for drag and drop using the OnMOuse* routines, and there is an example of Raycasting further down the page.

It looks like you should use Raycast.

http://docs.unity3d.com/Documentation/ScriptReference/Collider.Raycast.html

Just attach that script to the object you want to be able to select, edit the code to include a check for mouse down, and set the bool to true if everything checks out.