editable 3d text?

You can use a hidden TextField and copy the text into a 3d-text GameObject. It's a bit of a workaround as the 3d-text isn't made to be editable directly - but Unity always finds a way.

I cooked up a little script for you to get you started:

 /*  3d-Text Edit
     Editable 3d-text object.
     Put this script on a 3d-text GameObject.
     Note: Make sure to have a collider on the GameObject to register Raycasts
 */
 
 private var inEditMode : boolean = false;
 private var storedString : String;
 private var textComponent : TextMesh;
 private var guiString : String;
 
 function Start () {
     //Store the String
     textComponent = GetComponent(TextMesh);
     storedString = textComponent.text;
     guiString = storedString;
     
     //Visual Aid for Focus (example)
     renderer.material.color.a = 0.5;
     
     checkChars();    //Check so that the 3d-text isn't empty
     fitCollider();    //Set the Collider to fit the 3d Text Size
 }
 
 function OnGUI () {
     if(inEditMode) {
         //Make a TextField which sends to the 3d-text GameObject
         GUI.SetNextControlName ("hiddenTextField"); //Prepare a Control Name so we can focus the TextField
         GUI.FocusControl ("hiddenTextField");        //Focus the TextField
         guiString = GUI.TextField (Rect (90, -100, 200, 25), guiString, 25);    //Display a TextField outside the Screen Rect
         
         //Listen for keys
         if (Input.anyKey) {
             textComponent.text = guiString;    //Set the 3d-text to the same as our hidden TextField
             fitCollider();     //Resize the Collider
         }
     }
     //Begin Edit on RightClick
     if (Input.GetMouseButtonDown(1)) {
         var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
         var hit : RaycastHit;
         if (Physics.Raycast (ray, hit)) {
             if(hit.transform==transform) {
                 inEditMode = true;
                 renderer.material.color.a = 1;    //Alpha 100% on selection
             }  else {
                 inEditMode = false;
                 renderer.material.color.a = 0.5;    //Alpha 50% on deselection
                 checkChars();    //Check so the 3d-text isn't empty
             }
         }
     }
     //Exit Edit on KeyCode Return or Escape
     if (inEditMode && Input.GetKeyDown(KeyCode.Return) || inEditMode && Input.GetKeyDown(KeyCode.Escape)) {
         inEditMode = false;
         renderer.material.color.a = 0.5;    //Alpha 50% on deselection
         checkChars();    //Check so the 3d-text isn't empty
     }
 }
 
 //Set the Collider to fit the 3d Text Size
 function fitCollider () {
     collider.size.x= renderer.bounds.size.x;
     collider.size.y= renderer.bounds.size.y;
 }
 
 //Check the Size of the 3d-text
 function checkChars () {
     if(textComponent.text.ToCharArray().Length==0) {
         textComponent.text = "NULL";
             fitCollider();
     }
 }
 
 /*
 //If you want inEditMode on Left Click use this function instead of manual Raycasting
 function OnMouseDown () {
     inEditMode = true;
 }
 */

Feel free to ask if I left something you wonder uncommented.

References for this method: GUI-Class, GUI.SetNextControlName, GUI.FocusControl, GUI.TextField, Input-Class, Input.anyKey Physics.Raycast, RaycastHit